The French tax notice arrives in the summer, or a separate tax roll follows in the autumn, and a line you have never seen in Britain is waiting for you: CSG, CRDS, sometimes CASA, charged on the UK State Pension, a SIPP or a company scheme. After Brexit many British residents assumed an S1 form, or the France–United Kingdom tax treaty, would keep French social charges off a British pension. Income tax on a UK pension and social charges on that pension are not the same thing, they do not travel on the same form, and they are not challenged in the same office.

CSG is the contribution sociale généralisée, a general social contribution. CRDS is the contribution pour le remboursement de la dette sociale. CASA is the contribution additionnelle de solidarité pour l’autonomie, an extra 0.3 per cent charge on certain pensions. France treats a retirement pension as a revenu de remplacement, a replacement income. Whether those charges attach to a British pension depends on two cumulative gates in article L. 136-1 of the Social Security Code (code de la sécurité sociale): French tax residence, and being “à la charge” of a compulsory French health-insurance scheme. Miss either gate and the charge is not due. Pass both, and the tax office may collect CSG on the UK pension by tax roll, even where the British payer never withheld a euro. The pages below set out the test, the rates, the collection channel and the claim, with each decisive rule tied to the official text.

I. When does France charge CSG on a UK pension after Brexit?

A. Tax residence and French health-insurance affiliation: the two-gate test

The starting point is not the treaty and not the S1. It is the personal scope of CSG on activity and replacement income. Article L. 136-1 of the Social Security Code states: “Il est institué une contribution sociale sur les revenus d’activité et sur les revenus de remplacement à laquelle sont assujettis : 1° 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 ;”. In plain English, CSG on replacement income is due only from people who are both treated as French tax residents for income tax and, in any capacity, covered by a compulsory French health-insurance scheme. The same double condition is the gateway for CRDS on those incomes, because the Cour de cassation, France’s highest ordinary court, has held that article 14 of ordinance no. 96-50 of 24 January 1996 refers back to article L. 136-1.

Tax residence is defined by article 4 B of the General Tax Code (code général des impôts): “Sont considérées comme ayant leur domicile fiscal en France au sens de l’article 4 A : a. Les personnes qui ont en France leur foyer ou le lieu de leur séjour principal ;”. The foyer is the permanent home. The séjour principal is the main place of stay, in practice often more than 183 days in the calendar year, although the statute does not write that number into article 4 B. An activity exercised in France, unless it is accessory, and the centre of economic interests, complete the domestic tests. A person who meets one of those tests is still not a French resident where a double-tax treaty treats them as resident only of the other State. That last sentence of article 4 B, paragraph 1, matters for couples split between Kent and the Dordogne: the treaty tie-breaker can take you out of French tax residence, and with it out of CSG on replacement income. The mechanics of proving that split are set out in our guide on British couples split between France and the UK.

The second gate is social-security affiliation, not the mere fact of living in France and seeing a French doctor. PUMA, the protection universelle maladie, is the universal sickness cover in article L. 160-1 of the Social Security Code: anyone working in France, or residing there on a stable and regular basis without working, has their health costs taken in charge. That is a right to care. CSG on a pension asks a narrower question: are you “à la charge”, in any capacity, of a compulsory French health-insurance scheme? A British pensioner who has registered an S1, the portable document that lets the UK remain the competent State for healthcare while you live in France, is receiving French care for the account of the British system. The S1 is not, by itself, proof that you are a member of the French scheme for contribution purposes. The French liaison body, the Cleiss (Centre des liaisons européennes et internationales de sécurité sociale), describes the S1 as the document that allows the insured person living in a State other than the competent State to register with the health-insurance institution of the place of residence in order to receive benefits in kind. GOV.UK’s living-in-France healthcare guidance still tells UK nationals to register a UK-issued S1 with the local CPAM, the caisse primaire d’assurance maladie, the local health-insurance fund. Registration for care and affiliation for CSG must not be confused.

The Cour de cassation drew the opposite conclusion where the pensioner also held a French State pension. In Cass. 2e civ., 9 December 2010, no. 09-71.814, a man received a French general-scheme old-age pension and an EPO pension on which he paid compulsory sickness contributions to that international organisation. He argued that he was not “à la charge” of a French compulsory scheme. The Court rejected the appeal in these terms: “ayant constaté que M. X… qui n’exerçait plus d’activité salariée, était fiscalement domicilié en France et percevait une pension vieillesse du régime général français, et qu’il était dès lors, par application de l’article L. 311-9 du code de la sécurité sociale, pris en charge par un régime obligatoire français d’assurance maladie, la cour d’appel en a déduit à bon droit, qu’il remplissait les conditions d’assujettissement à la CSG fixées par l’article L. 136-1 de ce code auquel renvoie pour la CRDS l’article 14 de l’ordonnance n° 96-50 du 24 janvier 1996 modifiée, peu important les prestations maladie dont il pouvait bénéficier auprès de l’OEB”. Holding a French old-age pension was enough, at that time under article L. 311-9, to place him in the French scheme “in any capacity”, even if another scheme actually paid his medical bills. A British resident who also draws a small CNAV or Agirc-Arrco pension is in a different legal box from the S1-only State Pensioner.

The uniqueness principle of European social-security coordination still colours the analysis for people who remain inside it. In Cass. 2e civ., 25 September 2025, no. 22-24.634, published in the Bulletin, the Second Civil Chamber recalled that Regulations 1408/71 and 883/2004 “consacrent le principe d’unicité de la législation de sécurité sociale, selon lequel la personne à laquelle les règlements s’appliquent n’est soumise qu’à la législation d’un seul État membre, en sorte que celle-ci, affiliée à un régime de sécurité sociale d’un État membre, ne doit pas contribuer au régime de sécurité sociale d’un autre État membre (CJUE, arrêt du 26 février 2015, De Ruyter, C-623-13, point 35)”. De Ruyter was about contributions on investment income. The 2025 judgment uses it for the single-legislation principle. After Brexit that principle does not apply automatically to every British resident. People who were already in a cross-border situation at the end of the transition period may still be inside the Withdrawal Agreement. People who moved later may fall under the Trade and Cooperation Agreement’s social-security protocol. Neither instrument turns a UK pension into French replacement income by magic. Both are relevant only once article L. 136-1’s two gates have been tested on the facts of the year in dispute.

The public pension service, CNAV, the Caisse nationale d’assurance vieillesse, the national old-age insurance fund, repeats the same two conditions in administrative language for a taxpayer whose tax home is in France: membership of a compulsory French health-insurance scheme, and a revenu fiscal de référence, the reference tax income shown on the tax notice, above the published threshold. A British reader should therefore ask two factual questions before arguing about rates: were you French tax resident in the year of payment, and were you, that year, a member of a compulsory French health-insurance scheme? An S1-only Withdrawal Agreement resident who never drew a French pension and never paid PUMA contributions is usually fighting the second gate. A resident who worked in France, who holds a French pension, or who was affiliated to PUMA, is usually inside the charge and must fight the rate, the base and the collection.

B. Which UK pensions are in the base, at which rate, and how the tax office collects

Once both gates are open, the base is wide. Article L. 136-1-2 of the Social Security Code provides: “La contribution prévue à l’article L. 136-1 est due sur toute somme destinée à compenser la perte de revenu d’activité, y compris en tant qu’ayant droit, et versée sous quelque forme que ce soit et quelle qu’en soit la dénomination.” Any sum intended to make good the loss of earned income, including as a dependant, in any form and under any name, is in principle CSG replacement income. A UK State Pension, a defined-benefit occupational pension, a SIPP in payment and a survivor’s pension can all meet that definition. The label on the British payslip does not control the French characterisation.

The standard CSG rate on pensions is not the 9.2 per cent that applies to wages. Article L. 136-8 of the Social Security Code, in the version in force from 27 June 2026, states: “Sont assujetties à la contribution au taux de 8,3 % les pensions de retraite, et les pensions d’invalidité.” By derogation, article L. 136-8 III applies a 3.8 per cent rate where the reference tax income of year N-2, defined by article 1417, IV of the General Tax Code, sits between the lower and upper bands written in that paragraph. Article L. 136-8 III bis applies 6.6 per cent in the intermediate band. Article L. 136-8 III ter revalues those bands on 1 January each year in line with consumer prices excluding tobacco. Article L. 136-1-2, II, 1° excludes from the CSG base altogether the retirement and invalidity pensions of people whose year N-2 reference income does not exceed the threshold in article L. 136-8 III, 1°, and the holders of certain non-contributory old-age or invalidity benefits. The practical result is four CSG outcomes on a pension: nil, 3.8 per cent, 6.6 per cent or 8.3 per cent. The bands on your avis d’impôt, the tax notice, and on the current service-public table are the ones to use for the year in dispute. Do not copy a neighbour’s 2024 figures onto a 2026 bill.

CRDS and CASA sit on top. The Cour de cassation, in the 2010 judgment already cited, treats article 14 of ordinance no. 96-50 as the CRDS gateway on replacement income, by reference to article L. 136-1. The State pension service states the CRDS rate on a pension as 0.50 per cent. Article L. 137-41 of the Social Security Code creates CASA: “Est instituée une contribution additionnelle de solidarité pour l’autonomie au taux de 0,3 %, assise sur les avantages de retraite et d’invalidité ainsi que sur les allocations de préretraite qui ne sont pas assujettis aux prélèvements mentionnés à l’article 235 ter du code général des impôts et qui sont perçus par les personnes physiques désignées à l’article L. 136-1 du présent code.” CASA is 0.3 per cent, on retirement and invalidity benefits, payable by the same people who are inside article L. 136-1. Paragraph II of the same article excludes pensions where the reference income does not exceed the article L. 136-8 III, 2° ceiling, which is why CASA is not due at the reduced 3.8 per cent CSG rate. The State civil-service pension service confirms that CASA is withheld only if you are on the 6.6 or 8.3 per cent CSG rate. Added together, a pensioner on the full CSG rate is looking at 8.3 + 0.5 + 0.3 = 9.1 per cent of the gross pension, before any income tax.

Part of the CSG is deductible for income tax. Article 154 quinquies of the General Tax Code provides that CSG on activity and replacement income is allowed as a deduction “à hauteur de 4,2 points lorsqu’elle est prélevée au taux de 6,6 % et à hauteur de 5,9 points lorsqu’elle est prélevée au taux de 8,3 %”, and 3.8 points where it is levied at 3.8 per cent. The deductible fraction is not a refund of the social charge. It only reduces the income-tax base of the year in which the CSG was paid. A British reader who wins a CSG discharge must also watch the knock-on effect on the following year’s income tax.

Not every British “pension” payment is CSG replacement income. In Cass. 2e civ., 8 October 2020, no. 19-16.078, published in the Bulletin, the Court held: “Il résulte de ces dispositions que n’entrent pas dans l’assiette de la contribution sur les revenus d’activité et de remplacement perçue au titre de la CSG et de la CRDS, ni dans celle de la cotisation due au titre des assurances maladie, maternité, invalidité, décès, les sommes versées au bénéficiaire d’un contrat de retraite supplémentaire à cotisations définies qui exerce la faculté de rachat prévue à l’article L. 132-23, alinéa 2, du code des assurances, dans sa rédaction applicable au litige.” A buy-back of a defined-contribution supplementary contract under the then insurance-code rule was outside the CSG/CRDS replacement-income base. A UK lump sum is a different animal, with its own French options, which we have already mapped in the guide on the UK pension lump sum, the 7.5 per cent option and the S1. Do not assume that a PCLS, a pension commencement lump sum, is taxed as a French pension instalment. Characterise the payment first, then ask whether article L. 136-1-2 can bite.

Income tax and CSG also follow different international rules. Article 18 of the France–United Kingdom tax treaty of 19 June 2008, published by decree no. 2010-20 of 7 January 2010, provides that, subject to article 19(2) on certain public-service pensions, pensions and similar remuneration paid to a resident of a contracting State in respect of past employment are taxable only in that State. A private pension paid to a French resident is, as a rule, taxable only in France. Article 19(2) keeps certain government-service pensions in the paying State. That allocation is about income tax. It does not, by itself, wipe out CSG. The tax administration’s rescript BOI-RES-RSA-000219 of 11 August 2025 states that, subject to the relevant tax treaty, social charges on replacement income apply whether the pension is French or foreign, and whether it is paid as an annuity or as capital, provided the two gates of article L. 136-1 are met. How to declare the UK pension for income tax, and how to claim any UK tax credit, is a separate exercise, set out in our article on UK private pensions in France after Brexit.

Collection of the foreign slice is not done by CNAV. French payers withhold CSG at source. A UK scheme does not. Article L. 136-5, II bis, of the Social Security Code states: “La contribution due sur les revenus de source étrangère, sous réserve s’agissant des revenus d’activité qu’elle n’ait pas fait l’objet d’un précompte par l’employeur, et la contribution sur l’avantage mentionné au I de l’article 80 bis du code général des impôts , ainsi que sur l’avantage mentionné au I de l’article 80 quaterdecies du même code lorsque ce dernier est imposé à l’impôt sur le revenu suivant les règles de droit commun des traitements et salaires, sont établies, recouvrées et contrôlées dans les conditions et selon les modalités prévues au III de l’article L. 136-6 du présent code.” Foreign-source CSG is assessed, recovered and audited like the contribution on investment income. Article L. 136-6, III then says: “La contribution portant sur les revenus mentionnés aux I à II, à l’exception du e bis du I, est assise, contrôlée et recouvrée selon les mêmes règles et sous les mêmes sûretés, privilèges et sanctions que l’impôt sur le revenu.” The foreign pension CSG therefore arrives as a tax roll, a rôle, from the direction générale des finances publiques, the public-finance directorate, not as a line on a CNAV payslip. That is why so many British residents only discover the charge when the tax notice or a separate assessment is issued, months after the UK pension was paid gross.

Where the pensioner is inside the French scheme and also receives a French pension, Europe does not cap the French charge at the French slice. The Conseil d’État, the highest French administrative court, held in CE, 25 October 2024, no. 473997: “Ces dispositions, dont la lettre est claire, n’interdisent pas à l’Etat membre compétent d’assoir les cotisations sur la totalité des pensions perçues de deux ou plusieurs Etats membres par une même personne, pas plus qu’elles ne lui imposent de limiter le montant des cotisations à hauteur du montant de la pension qu’il verse.” If you are the competent State’s pensioner, CSG can be computed on the UK pension plus the French pension. The argument that France may charge only on the French slice is the argument the Conseil d’État rejected. The S1-only file and the mixed-pension file are therefore won or lost on different grounds: affiliation for the first, rate, base and collection for the second.

II. How to challenge a CSG bill on a UK pension and recover an overcharge

A. The tax-roll claim, the social-security claim, and the deadlines

Identify the document before you identify the court. If CSG was withheld by a French pension fund on a French pension, the dispute follows social-security procedure. Article L. 136-5 provides that disputes arising from the charging of the contribution on the incomes mentioned in articles L. 136-1 to L. 136-4 “relèvent du contentieux de la sécurité sociale et sont réglés selon les dispositions applicables aux cotisations de sécurité sociale”. That path starts with the commission de recours amiable, the friendly-settlement commission of the fund, then the pôle social of the tribunal judiciaire, the social division of the ordinary court. Appeals from those judgments lie to the social chamber of the court of appeal, then to the Second Civil Chamber of the Cour de cassation. A British resident whose only complaint is the CSG line on a CNAV or Agirc-Arrco payslip is in that world.

If the charge is on a UK pension, article L. 136-5, II bis, has already sent you into the tax world of article L. 136-6, III. The claim is then a réclamation contentieuse, a formal tax claim, against the roll or the assessment. Article R.* 196-1 of the Tax Procedures Book (livre des procédures fiscales), in the version in force from 30 July 2026, states: “Pour être recevables, les réclamations relatives aux impôts autres que les impôts directs locaux et les taxes annexes à ces impôts, doivent être présentées à l’administration au plus tard le 31 décembre de la deuxième année suivant celle, selon le cas : a) De la mise en recouvrement du rôle ou de la notification d’un avis de mise en recouvrement ;”. The ordinary time-limit is 31 December of the second year after the year in which the roll was put into collection or the recovery notice was notified. If you paid without a roll, the clock can run from the payment. Do not wait for a “final” conversation with the local tax centre. A letter that merely asks for an explanation is not a réclamation. The claim must ask for discharge or reduction of a stated amount, for a stated year, on a stated legal ground, and it must be filed with the service that issued the assessment.

The file you attach is as important as the deadline. For an S1-only challenge, the core exhibits are the S1 or its UK equivalent covering the year of payment, the CPAM registration letter if you have one, proof that you held no French pension that year, the tax notice showing French residence, and the roll or notice that charged CSG on the UK pension. For a rate challenge, the exhibits are the avis d’impôt of year N-1 showing the revenu fiscal de référence of year N-2, the household quotient, and the CSG rate actually applied. For a base challenge, you need the UK scheme’s breakdown: State Pension, taxable pension, tax-free lump sum, death benefit, return of contributions. A single annual sterling total, converted at a random rate, is how overcharges are born. Convert at the Bank of France annual average rate used for the income-tax return, and keep the sterling payslips.

If the administration rejects the réclamation or does not answer within the statutory time, the next step for a tax-roll CSG is the tribunal administratif, the administrative court, of the place of your tax residence. Paris residents file with the Tribunal administratif de Paris. Residents of the inner suburbs file with the court of their département. That is a national procedure with a local registry, not a special “British” track. The pôle social of the Tribunal judiciaire de Paris remains the right court only for the withheld French-pension dispute. Mixing the two paths is a classic way to lose six months. If both a French fund and the tax office have charged you, you may need both claims, each limited to the slice that office collected.

A refund is not automatic the day the court writes your name. After a successful réclamation the tax office issues a dégrèvement, a discharge, and then a repayment. After a successful social-security claim the fund is ordered to repay the sums unduly withheld, often with legal interest. Check the following year’s CSG rate: a discharge that lowers year N’s reference income can change year N+2’s band. Check also the income-tax deduction under article 154 quinquies. If CSG is repaid, the corresponding deduction may have to be reversed. Ask for the two adjustments in the same correspondence so that one victory does not create a second bill.

B. S1-only pensioners, mixed French and UK pensions, and the mistakes that lose the refund

The S1-only file is won on affiliation, not on sympathy. The administration will say that you live in France, that you have a carte vitale, the plastic health card, and that PUMA therefore makes you “à la charge” of the French scheme. Your answer is article L. 136-1 itself: the statute requires a compulsory French health-insurance scheme, not mere residence and not mere access to care. The S1 is the document by which the United Kingdom remains competent for healthcare. GOV.UK still instructs UK nationals living in France to register that form with CPAM. Our earlier article on S1 healthcare and reimbursement before CPAM registration deals with the care side. On the contribution side, produce the S1 for each disputed year, the UK pension award letter, and a negative statement from CNAV or from your French tax file showing no French pension. If the tax office cannot point to a French compulsory scheme that actually covered you that year, the second gate of article L. 136-1 fails and CSG, CRDS and CASA on replacement income are not due.

The mixed-pension file is the one in which the 2010 Cour de cassation judgment and the 2024 Conseil d’État decision cut the other way. A British resident who also receives a French old-age pension is, on the 2010 reasoning, inside the French scheme by the very fact of that pension. The Conseil d’État then allows the competent State to compute contributions on the whole of the pensions, French and foreign. In that situation the productive challenges are different. First, the rate: a household just above a band can drop into 6.6 per cent or 3.8 per cent, or into the article L. 136-1-2 exemption, once a deductible CSG fraction, a family quotient or a corrected foreign-income figure is restored. Second, the base: a UK tax-free lump sum, a return of non-taxed contributions, or a payment that is not a replacement income at all, must be taken out before 8.3 per cent is applied. Third, double collection: CNAV has no mandate to withhold CSG on the UK slice, and the tax office has no mandate to collect again what a French fund already withheld on the French slice. Fourth, the year: CSG follows the year of payment of the pension, while the rate follows the reference income of year N-2. A newly arrived resident whose first French notice uses a UK-only reference year is often on the wrong band.

Visitor-card retirees sit in a third box. A carte de séjour visiteur, a visitor residence card, is built on the promise that you will not work in France and that you have comprehensive health cover. Many British visitors use private insurance rather than S1. If they are not members of a French compulsory scheme, article L. 136-1 should keep CSG off the UK pension even if they are French tax residents. The risk is the opposite mistake: CPAM or URSSAF, the social-contribution collector, later claiming a PUMA affiliation and a cotisation subsidiaire, a subsidiary health contribution, because the private policy was not accepted as equivalent. That is a different bill from CSG on the pension, and it is fought with different texts. The residence-card side is covered in our guide on renewing a British retiree’s visitor card. Do not answer a PUMA recovery notice with a CSG réclamation, or a CSG tax roll with a visitor-card appeal.

Several recurring errors destroy otherwise good claims. The first is to argue that the treaty allocates pensions to France for income tax and that CSG is therefore double tax. Article 18 allocates income tax. CSG on replacement income is a social-security contribution in French law, collected like income tax when the income is foreign, but it is not the income tax that article 18 distributes. The second is to send the S1 to HMRC and assume the French tax office has seen it. The tax roll is issued from the French file. The S1 must be in that file, for the year of payment, not merely in a CPAM drawer from 2021. The third is to miss the 31 December N+2 deadline in article R.* 196-1 while waiting for a ministerial question or a forum answer. The fourth is to challenge the 2024 Conseil d’État position with a “cap at the French pension” theory that the Court has already rejected. The fifth is to treat a UK lump sum as if it were a monthly pension, or a monthly pension as if it were a lump sum: the 2020 Cour de cassation decision on a French supplementary buy-back shows that form still matters, but it is not a free pass for every capital payment. The sixth is to ignore CASA and CRDS. A claim that mentions only “CSG 8.3 per cent” leaves 0.8 per cent on the table, and CASA has its own exclusion in article L. 137-41, II.

Brexit does not freeze the picture. A person who moved to France before the end of the transition period, who has lived there continuously and who holds a Withdrawal Agreement residence card, remains inside a coordinated healthcare system in which the S1 still has its original meaning. A person who moved in 2024 on a long-stay visitor visa, without an S1, may be pushed towards PUMA and then towards CSG because the second gate of article L. 136-1 is then easier for the administration to claim. The legal test does not change with the newspaper headline. What changes is the evidence that proves, for that calendar year, whether you were or were not “à la charge” of a compulsory French scheme. Keep the S1, the visa, the residence card, the CPAM letters, the URSSAF calls and every tax roll. The claim is won on that bundle, not on the word “Brexit”.

Conclusion

French CSG, CRDS and CASA on a UK pension are not a single “social tax” that every British resident must pay. Article L. 136-1 still requires both French tax residence and membership of a compulsory French health-insurance scheme. An S1-only pensioner who never entered the French scheme has a direct statutory argument against the charge on replacement income. A mixed French and UK pensioner is usually inside the charge, may be assessed on the whole of the pensions following the Conseil d’État’s 2024 ruling, and must fight the rate, the base and the collection channel. Foreign-source CSG is collected by the tax office on a roll, under articles L. 136-5, II bis and L. 136-6, III, and is challenged by a tax réclamation within the article R.* 196-1 time-limit. French-source CSG withheld by a fund remains a social-security dispute. The treaty decides where income tax is due. It does not, by itself, decide CSG. If a notice or a roll has already been issued, the useful work is to match the document to the right procedure, assemble the S1 and the pension breakdown for the year in dispute, and file before 31 December of the second year. That is the point at which a telephone review of the papers is worth more than another conversion of the sterling total.

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