You are retired, you live in France, and every four weeks a payment lands from Newcastle. The British State Pension — the flat-rate pension paid by the United Kingdom to people with enough National Insurance contribution years — follows you to France, but the French tax office (the service des impôts des particuliers) expects to see it on your French tax return. Many British residents get this wrong in both directions: some keep paying UK tax on a pension that France alone is entitled to tax, and others declare the pension in France but forget the social charges question, or pay social charges they do not owe. Since Brexit, the questions have multiplied, because residence rights now sit under the Withdrawal Agreement while tax and social security coordination follow their own instruments. This article explains, step by step, where your British State Pension is taxed when you live in France, how to declare it on the French forms 2047 and 2042, when the French social charges (the contribution sociale généralisée, CSG, and the contribution pour le remboursement de la dette sociale, CRDS) apply and when the S1 healthcare certificate exempts you, and how to challenge a wrong tax bill or a wrong social-charge levy. It covers the State Pension paid for your own contribution record, including the frozen-rate rule for pensioners abroad, and explains where the analysis differs for a French pension earned in France, for a UK civil-service pension, and for a surviving spouse. Each legal proposition below is tied to the official text or decision it comes from, so you can check it and, if needed, put it in front of the administration or a judge.

I. Where your British State Pension is taxed and how France taxes it

The starting point is simple, and it surprises many new arrivals: when you are resident in France for tax purposes (a résident fiscal français), your British State Pension is normally taxable only in France. The United Kingdom gives up its right to tax it, France picks it up in full, and the UK should pay it gross of UK tax once the treaty position is established. The difficulty is entirely practical — obtaining the residence position, operating the treaty mechanism with His Majesty’s Revenue and Customs (HMRC), and then declaring and computing the French tax correctly. The two sub-sections below take each stage in turn.

A. The treaty rule: France taxes you if you live in France — and how to declare the pension on forms 2047 and 2042

French domestic law casts the net very wide before the treaty allocates the catch. Article 79 of the French General Tax Code (code général des impôts) provides that “Les traitements, indemnités, émoluments, salaires, pensions et rentes viagères concourent à la formation du revenu global servant de base à l’impôt sur le revenu.” In plain English: pensions, including foreign pensions, feed into the worldwide income (the revenu global) on which French income tax (the impôt sur le revenu) is computed when you are domiciled in France for tax purposes. Domicile here is the tax-home concept of the French tax code — broadly, your main home, your principal sojourn, your professional activity or the centre of your economic interests being in France. If France is your tax home, you declare your worldwide income in France, and the British State Pension is inside that worldwide base unless a treaty says otherwise.

The treaty does say something decisive, and it says it in France’s favour. The double tax convention (the convention fiscale) signed in London on 19 June 2008 between the United Kingdom and France, in force since 18 December 2009, allocates taxing rights pension by pension. Article 18 of that convention, published on GOV.UK, gives the exclusive right to tax employment-linked pensions to the country where the pensioner lives. Read the mechanism slowly, because every element matters. The employment link covers the State Pension built up through National Insurance contributions during working life. The residence test points at you, living in France. Exclusivity means France alone taxes the pension once you are French-resident. The pension is therefore not split between the two countries and not taxed twice: the United Kingdom exempts it, France taxes it under its own rules, and the treaty’s elimination-of-double-taxation article makes sure any UK tax wrongly deducted can be relieved.

Two boundaries need marking immediately, because readers constantly mix them up. First, Article 18 is expressly made subject to paragraph 2 of Article 19, the government-service article (the pensions paid for work done directly for the British state, a local authority or a statutory body — the classic civil-service pension). If your pension is a UK civil-service, armed-forces, police, teacher-in-state-school or National Health Service pension paid out of public funds for government service, Article 19 may keep the taxing right in the United Kingdom, with France giving a credit instead of taxing outright. The State Pension — the Department for Work and Pensions pension paid from Newcastle on the basis of your National Insurance record — is not a government-service pension in this sense, and it stays under Article 18. If you receive both a State Pension and a civil-service pension, the two follow different articles, and each must be entered on the correct line of the return. Second, the treaty allocates the right to tax; it does not tell France how much tax to charge. Rates, allowances and the mechanics of the return are purely French domestic law, examined in the next sub-section.

On the British side, the pension can arrive with UK tax already deducted through Pay As You Earn (PAYE), the British withholding system for pensions and salaries, because HMRC does not automatically know you have become French-resident. The remedy is the treaty claim: you notify HMRC that you are resident in France and claim exemption from UK tax on the pension under Article 18, typically on the DT-Individual France claim form, supported where asked by a certificate of French residence (the attestation de résidence fiscale) from the French tax office. Once HMRC accepts the claim, the State Pension is paid without UK deduction and a Notice of Coding (the avis de codification that tells the payer how much tax to withhold) is adjusted. Any UK tax over-deducted before the claim succeeded is reclaimed from HMRC for the years concerned; it is not credited in France, because France taxes the gross pension in full and the treaty gives France the exclusive right. Keep every HMRC letter, because the French inspector (the vérificateur) sometimes asks why no foreign-tax credit is claimed, and the answer — exclusive French taxation under Article 18 — must be documented.

On the French side, the declaration obligation (the obligation déclarative) is personal, annual and inescapable. Article 170 of the General Tax Code provides that “toute personne imposable audit impôt est tenue de souscrire et de faire parvenir à l’administration une déclaration détaillée de ses revenus et bénéfices” — every person liable to income tax must file a detailed return of income with the administration. For a British State Pension received by a French resident, the return has two layers. The pension is first detailed on appendix 2047 (the déclaration des revenus encaissés à l’étranger, the return for income received from abroad): the tax administration’s own guidance presents this appendix as the schedule detailing income received abroad — salaries, pensions, rental income, dividends, interest and similar items — as recalled on the impots.gouv.fr page on foreign-source income, and the service-public.fr page for declaration 2047 of income received abroad confirms the form’s role for taxpayers domiciled in France with income from outside mainland France. You enter the gross annual State Pension in pounds converted to euros at the rate applicable for the year, identify the United Kingdom as the source state, and tick the treaty position that the income is taxable in France. The totals are then carried across (the report) onto the main return 2042 (the déclaration d’ensemble des revenus), in the pensions boxes (cases 1AL and 1BL for the declarants’ pensions, the cases 1AL / 1BL), so that the pension joins the household’s taxable base. A frequent and expensive error is to enter the pension net of UK withholding rather than gross, or to omit the 2047 and enter only the 2042, which deprives the administration of the source information and can trigger an inquiry (a demande d’éclaircissements). Declare gross, declare the source, keep the DWP annual statement (the relevé annuel) and the exchange-rate calculation with the return’s supporting papers (the justificatifs).

One British peculiarity must be understood before computing anything: the frozen-rate rule (the pension gelée). The GOV.UK guidance on State Pension rates abroad explains that the pension is uprated each year only for residents of the United Kingdom, the European Economic Area, Gibraltar, Switzerland and a list of countries with specific agreements — and that France is within the uprated group while many other countries are not. Because France is covered, a British pensioner living in France continues to receive the annual increases, unlike a pensioner in, say, Australia or Canada whose pension is frozen at the departure rate. The GOV.UK page on the new State Pension for people who have lived or worked abroad adds that the amount remains based on the National Insurance record, including years that can be aggregated with work in France under the Withdrawal Agreement’s social-security coordination. Practically, this means the figure you declare in France each year moves with the triple lock (the triple verrouillage uprating mechanism), and a sudden jump in the euro amount on the 2047 between two years is normal, not an error — though you should still reconcile it against the DWP statement before filing.

B. How France calculates the tax: gross pension, 10 per cent allowance and your marginal rate

Once the pension is in the French base, France taxes it like a French pension, with the standard allowance (the abattement) and the household quotient (the quotient familial). The mechanics matter because they determine whether a modest State Pension produces any French tax at all, and because errors in this computation are the easiest to challenge with a calculator and the statute book.

The computation starts from the gross pension and applies the 10 per cent pensions allowance. Article 158, 5, a of the General Tax Code provides that “Les pensions et retraites font l’objet d’un abattement de 10 % qui ne peut excéder 4 439 €.” In English: pensions and retirement income benefit from a 10 per cent deduction capped at 4,439 euros per household, with a minimum floor amount per pensioner that is revised each year. The tax is then computed on the net amount — Article 82 of the General Tax Code provides that “il est tenu compte du montant net des traitements, indemnités et émoluments, salaires, pensions et rentes viagères” — so the allowance operates before the scale is applied. The allowance is automatic — you declare the gross pension and the administration applies the deduction — but you should verify it on the assessment notice (the avis d’imposition), because returns filed with the pension entered in the wrong box sometimes miss it. Note the cap is per household (the foyer fiscal), not per pension: a couple where each spouse receives a British State Pension shares the single ceiling, and the floor operates per pensioner. The allowance applies to the State Pension exactly as it applies to a French basic pension (the retraite de base) or a French complementary pension (the retraite complémentaire); there is no discrimination between a Newcastle pension and a Carsat pension at this stage.

The net pension after the allowance joins the household’s total net income alongside any other revenue — a French pension, rental income (the revenus fonciers), investment income — and the progressive scale (the barème progressif) applies by slices (the tranches) after division by the number of family shares (the parts de quotient familial): one share for a single person, two for a married couple or a civil-partnership couple (the partenaires de Pacs), plus half-shares for children. A single British pensioner in France whose only income is a full new State Pension of roughly 11,500 pounds a year will therefore typically owe little or no French income tax after the 10 per cent allowance and the tax-free slice, while a couple with two full State Pensions plus a British rental profit may find part of the pension taxed at 11 or 30 per cent at the margin (the taux marginal). Withholding at source (the prélèvement à la source) then spreads the payment: because DWP pays gross without French withholding, the French administration collects the tax through monthly instalments (the acomptes contemporains) computed from the last assessment, and a first-year resident with no prior French assessment pays the first year’s tax the following autumn on the assessment notice, then moves to instalments. If the instalments calculated by the administration assume income you no longer receive, or ignore the treaty position, they can be adjusted online (the gérer mon prélèvement à la source service) — and any overpayment is refunded on the next assessment.

Three calculation traps deserve special attention because they generate most of the disputes seen in practice. The first is the exchange rate (the taux de change): the pension must be converted to euros, and the administration accepts the annual average rate published for the year or the European Central Bank reference applied consistently; converting each four-weekly payment at its spot rate is also accepted if applied to all payments, but mixing methods within a year is not. Keep the rate source with your papers. The second is the additional pension elements (the éléments supplémentaires): the quarterly or annual statements sometimes show arrears (the arriérés) paid late, for example after a National Insurance record correction. Arrears relating to earlier years remain taxable in the year of receipt under French rules, subject to the special spreading system (the système du quotient) for exceptional income on request — do not simply omit them because they “belong” to another year. The third is the interaction with a French pension: where the household receives both a British State Pension and a French pension from the Caisse d’assurance retraite et de la santé au travail (Carsat, the French retirement fund), the 10 per cent allowance ceiling applies once to the total, and the treaty does not exempt the French pension from French tax. The assessment notice must therefore be read line by line: gross amounts, allowance, net global income (the revenu brut global), deductible charges, net taxable income (the revenu net imposable), gross tax, reductions and credits, net tax. An error at any line propagates, and each line has its own remedy, examined in Part II.

A final word in this part on proof (the preuve), because every challenge later depends on it. For each tax year, keep the DWP annual statement or the twelve monthly payslips, the HMRC treaty-claim acceptance or coding notice showing zero UK tax on the pension, the exchange-rate source, the filed 2047 and 2042 (download the PDF after online filing — the déclaration en ligne), and the assessment notice. Where a French pension also exists, keep the Carsat statement (the relevé de pension) showing the gross French pension and any French withholding. The courts decide pension cases on documents, not on recollection: the leading illustration is a British claimant whose French pension calculation turned on exactly which quarters in which countries counted, and the Cour de cassation (the French supreme court for civil matters) recorded at the outset that “après avoir exercé une activité professionnelle salariée au Royaume-Uni, en France et à Monaco, M. X…, ressortissant britannique né […] , a obtenu de la caisse d’assurance retraite et de la santé au travail du Sud-Est (la caisse), le bénéfice d’une pension de vieillesse” — Second Civil Chamber (the deuxième chambre civile), 7 November 2019, appeal No 18-18.344, dismissal (the rejet), a decision given after an earlier cassation of 9 March 2017 in the same dispute (appeal No 16-10.851, mentioned in the 2019 judgment itself). The lesson for every British reader is direct: cross-border careers produce fragmented records, the fund aggregates only what it is given, and the pensioner who keeps every statement from every country is the pensioner who can prove the missing quarter.

II. Healthcare, CSG-CRDS and what to do when the bill is wrong

Income tax is only half the levy. The other half is the French social charges on the pension — or, for many British S1 holders, the absence of those charges. Whether CSG and CRDS apply depends not on nationality and not on where the pension comes from, but on which country’s health system carries you. Hold the wrong certificate, or no certificate, and the charges appear; hold the S1 (the portable healthcare document) and register it correctly, and they fall away. This part explains the divide and then gives the complete challenge toolkit: administrative complaint, hierarchical appeal, mediation and the courts, with the deadlines that decide everything.

A. S1 holders pay no CSG or CRDS on the pension; PUMA residents do — and how CPAM registration works

The rule that decides everything fits in one sentence of statute. Article L. 136-1 of the Social Security Code (code de la sécurité sociale) provides that “Les personnes physiques qui sont à la fois considérées comme domiciliées en France pour l’établissement de l’impôt sur le revenu et à la charge, à quelque titre que ce soit, d’un régime obligatoire français d’assurance maladie” are liable to the contribution on employment and replacement income. Two cumulative conditions (the conditions cumulatives): tax domicile in France, and being covered — “à la charge” — by a compulsory French health-insurance scheme. Fail either condition and the CSG on replacement income (the revenus de remplacement, which include pensions) is not due. A British State Pensioner living in France plainly satisfies the first condition. The entire battle is over the second: are you carried by the French system, or by the British system through the S1?

The S1 (the document portable S1, the portable document that transfers healthcare competence) is the certificate by which the United Kingdom, as the state paying your State Pension, accepts the cost of your healthcare in France. The GOV.UK guidance on healthcare for UK nationals living in France explains that a resident in France who receives a UK State Pension or certain exportable benefits may be entitled to state healthcare paid for by the United Kingdom, and the National Health Service (NHS) guidance adds that an S1 entitles the holder and dependants to state healthcare paid for by the United Kingdom in the country of residence on the same basis as an insured resident of that country. Concretely, you apply to the NHS Business Services Authority for the S1 before or after the move, you present it to the local French health fund (the Caisse primaire d’assurance maladie, CPAM — the local branch of the French health insurance), and CPAM registers you as insured under French administration but at British expense (the affiliation sur critère de résidence avec prise en charge par le Royaume-Uni). The service-public.fr page on health insurance for a foreigner settling in France describes the registration routes including the S1, and its United Kingdom sections confirm that British nationals use the same S1 channel. Once registered, you are not “à la charge” of a compulsory French scheme within the meaning of Article L. 136-1: your cover flows from the British scheme via coordination, and the CSG and the CRDS on the pension fall away. The pension remains fully taxable in income tax — the S1 changes nothing on the 2047/2042 — but the 9.2 per cent CSG and 0.5 per cent CRDS that would otherwise attach to replacement income do not apply.

This is not administrative tolerance; it is the direct consequence of European coordination carried into the post-Brexit settlement, and the courts enforce it. The Versailles social chamber (the pôle social) recently applied exactly this test in a CSG dispute, opening its reasoning by recalling the two cumulative conditions of Article L. 136-1 — French tax domicile plus coverage by a compulsory French health scheme — and then testing the claimant’s affiliation step by step (Tribunal judiciaire de Versailles, social chamber, 30 September 2025, general register No 24/01284). The mechanism for proving the negative — proving you are not carried by the French scheme — is documentary: the paying bodies and the tax administration apply the exemption only against the S1 and its registration trace, under the detailed conditions set by Decree No 2019-633 of 24 June 2019 on the implementation of the CSG-CRDS exemption, published in the Journal officiel and the order (arrêté) of 29 July 2019 on the justificatory document for exemption from CSG and CRDS. In practice: obtain the S1 from the United Kingdom, register it at CPAM without delay, keep the CPAM attestation of registration (the attestation de droits) showing the British-competence code, and produce both documents to any body that levies the charges. The base of the contribution itself follows detailed computation rules: Article L. 136-2 of the Social Security Code opens with “Pour le calcul de l’assiette de la contribution prévue à l’article L. 136-1 du présent code”, and then sets the applicable treatment income by income. A pensioner who delays registration, or who registers under universal cover (the protection universelle maladie, PUMA) without presenting the S1, will be treated as French-carried for the interim period and charged accordingly — the exemption runs from proof, not from entitlement in the abstract.

The mirror image must be stated plainly, because early retirees and late S1 applicants constantly discover it too late. If you live in France, are tax-domiciled here, and are covered by the French universal health system without an S1 — the classic position of the British early retiree not yet at State Pension age, affiliated to PUMA through CPAM on residence grounds — then both conditions of Article L. 136-1 are met and the CSG-CRDS apply to your income including, once it starts, any pension in payment. Article L. 160-1 of the Social Security Code provides that “Toute personne travaillant ou, lorsqu’elle n’exerce pas d’activité professionnelle, résidant en France de manière stable et régulière bénéficie, en cas de maladie ou de maternité, de la prise en charge de ses frais de santé” — every person working, or residing in France in a stable and lawful manner when not working, is covered for health costs. That cover is a benefit with a price: the CSG on replacement income and, on capital income, thelevy under Article L. 136-6 of the Social Security Code on the contribution on capital income (revenus du patrimoine). When the State Pension age arrives and the S1 is issued and registered, the position flips from the registration date: the pension ceases to bear CSG-CRDS, while PUMA coverage continues for healthcare delivery at British expense. Dependants follow the S1 holder’s competence: a non-working spouse covered as the S1 holder’s dependant (the ayant droit) shares the exemption on replacement income, whereas a spouse with their own French employment record is assessed on their own affiliation. Mixed households should therefore map each person’s cover separately rather than assuming one S1 shields the whole house.

Two practical warnings complete the picture. First, the S1 exempts the pension from CSG-CRDS but never from income tax, and it never exempts French-source capital income taxed under Article L. 136-6 where the taxpayer is French-affiliated for that income — each levy has its own affiliation test, and a single certificate does not answer every question. Second, keep the paper chain continuous: the S1 itself, the CPAM registration attestation, the annual DWP statement, and the assessment notices showing which levies were or were not applied. Gaps in the chain are where money is lost — a three-month delay between arrival and CPAM registration is a three-month window in which the administration may treat you as French-carried, and only dated documents close it.

B. How to challenge: wrong tax, wrong social charges, wrong pension calculation — deadlines, letters and courts

Every error in this field has a remedy, but every remedy has a clock (the délai), and the clock starts from the document you hold. The challenge system (the contentieux) is staged: first the administration, then the mediator or the higher authority, then the judge. Skipping a stage or missing the date loses the case regardless of the merits, so this sub-section is organised as a strict sequence — what to file, where, and by when.

Start with the assessment notice, because most disputes are won at the reading stage. When the avis d’imposition arrives each late summer, reconcile it line by line against the return: gross British pension converted to euros, 10 per cent allowance applied within the household ceiling, correct number of shares, correct treaty position with no UK-tax credit claimed on the State Pension line, and — the decisive check — presence or absence of the CSG-CRDS lines (the prélèvements sociaux) consistent with your S1 position. If the notice taxes a pension that belongs to a different year, applies the allowance to only one spouse’s pension, counts the same pension twice (once on the 2047 carry-over and once as a manual entry), or levies CSG-CRDS despite a registered S1, the first step is the online complaint (the réclamation) through the personal account on impots.gouv.fr (the messagerie sécurisée) or by recorded-delivery letter (the lettre recommandée avec accusé de réception) to the local tax office (the service des impôts des particuliers, SIP) that issued the notice. The general deadline for contesting an income-tax assessment is 31 December of the second year following the year of the assessment — for a 2025 assessment on 2024 income, until 31 December 2027 — but social-charge complaints and withholding disputes follow their own shorter tracks, so file within weeks, not months, and always keep the acknowledgment. The complaint must state the facts, cite the text (Article 18 of the convention for exclusive French taxation, Article 158, 5, a for the allowance, Article L. 136-1 for the S1 exemption), attach the DWP statement, the HMRC treaty acceptance, the S1 and the CPAM attestation, and formulate a precise demand (the conclusion): discharge (the dégrèvement) of the overcharge, restitution of amounts levied, and recalculation of the instalments. An administration that does not answer within six months is deemed to have rejected the complaint (the rejet implicite), which opens the door to the court — do not wait indefinitely for a reply that the law treats as a refusal.

If the complaint fails, the second stage depends on the nature of the levy. For income tax and the social charges assessed on the tax notice, the appeal lies to the administrative court (the tribunal administratif) of your home: a petition (the requête) within two months of the express or implied rejection, with the assessment, the complaint and its evidence attached, and with each plea (the moyen) tied to a text or a documented fact. For CSG-CRDS levied by a collecting body outside the tax notice — typically URSSAF (the Union de recouvrement des cotisations de sécurité sociale et d’allocations familiales, the collection agency) or the pension fund itself — the route first passes through the amicable-appeals commission (the commission de recours amiable) of that body, usually within two months of the levy notification, before reaching the judicial social chamber (the pôle social du tribunal judiciaire), the specialist court that decided the Versailles CSG case cited above by testing affiliation against Article L. 136-1 line by line. For a French pension miscalculated by Carsat — missing British quarters, wrong rate, ignored coordination — the route is the fund’s own complaint, then the amicable-appeals commission, then the social chamber, with the Cour de cassation as the final reviewer of legal error, exactly as in the British claimant’s case that travelled from the fund to the Aix-en-Provence Court of Appeal (the cour d’appel) on referral after cassation and back to the Second Civil Chamber in 2019. At every stage, the file that wins is the file with continuous documents: without the S1, the CPAM attestation, the DWP statements and the assessment history, even a correct legal argument fails for want of proof.

Three recurring disputes deserve targeted tactics. First, double taxation in fact — UK withholding plus French assessment on the same pension. The remedy is sequential, not alternative: claim the treaty exemption from HMRC for the United Kingdom side and simultaneously complain in France that the gross pension is correctly assessed with no credit, attaching the HMRC claim and any UK repayment. Never claim a French foreign-tax credit (the crédit d’impôt) for UK tax on State Pension income that Article 18 reserves to France: the credit mechanism belongs to income that both states may tax, and invoking it on exclusively French-taxable income signals a misunderstanding that can delay the file by a year. Second, CSG-CRDS levied despite the S1. Here the decisive documents are the S1, the CPAM registration attestation with its date, and proof that the pension post-dates registration; the legal plea is the absence of the second condition of Article L. 136-1, supported by the decree and order on the justificatory documents. If the levy pre-dates registration, concede the interim period and contest only from the registration date — a partial claim argued honestly succeeds faster than a total claim argued against the documents. Third, the frozen-rate or missing-quarter pension: where DWP pays less than expected because the National Insurance record is incomplete, or where Carsat aggregates incorrectly across the United Kingdom, France and a third state, the remedy is a record correction first (HMRC National Insurance/payment history, voluntary contributions where available; Carsat career statement — the relevé de carrière — corrected with British employment evidence), and only then a legal challenge to the calculation. The 2019 Cour de cassation case is the cautionary tale: the British claimant contested the reduced-rate calculation for years, arguing aggregation across France, the United Kingdom and Monaco, and the Court dismissed the appeal (the rejet du pourvoi), leaving the fund’s calculation standing — because coordination aggregates only where the instruments provide for it, and Monaco quarters obey their own bilateral rules. Challenge the record early, challenge the law precisely, and never assume that every year worked anywhere counts everywhere.

Close with the calendar that governs all of it. The online return deadline (the date limite de déclaration) falls each May-June by residential zone; the assessment arrives in late summer; the complaint runs to 31 December of the second following year for income tax but far shorter for collection-body levies; the court petition runs two months from rejection; enforcement (the recouvrement forcé) by the administration is suspended on express request only where the claim is properly filed and, before the judge, on application for a stay (the sursis de paiement) with guarantees where required. File early, file in French or with a translation the office can process, number every attachment (the pièces), and keep every receipt. The British State Pension in France is a solved problem in law — exclusive French taxation, French computation, S1-based social-charge exemption — and every residual dispute is a problem of documents, dates and proper routing. Put the treaty article on the first page, the S1 on the second, and the numbers on the third, and the file decides itself.

Conclusion

A British State Pensioner living in France after Brexit occupies a clear and favourable position once the three instruments are kept apart. The 2008 convention gives France the exclusive right to tax the State Pension and takes the United Kingdom out of the picture; French domestic law then taxes the gross pension with the standard 10 per cent allowance inside the household’s progressive computation; and the S1, duly obtained from the British authorities and registered at CPAM, removes the pension from CSG and CRDS because the pensioner is no longer carried by a compulsory French scheme. Each stage has its form and its proof — the HMRC treaty claim and coding notice, the 2047 detailed appendix carried onto the 2042, the DWP statements with a consistent exchange rate, the S1 with its dated CPAM registration — and each error has its forum, from the online complaint to the administrative court and the social chamber. The pensioners who pay too much are almost never taxed under the wrong law; they are taxed on the wrong figure, in the wrong box, without the right certificate, or after the wrong deadline. Assemble the file before the administration asks for it, reconcile every assessment notice on arrival, and challenge quickly, precisely and with the official texts attached. France and the United Kingdom built a complete corridor for this pension — treaty, coordination, registration — and the pensioner who walks it with documents in hand keeps every pound the corridor promises.