Interest from a British savings account usually arrives in full, with no tax taken off. For a British citizen who has settled in France since Brexit, that gross payment looks like a small piece of good news: the high-street bank or building society (a member-owned British savings institution) pays the interest gross, no deduction appears on the statement, and nothing needs to be done. That impression is wrong, and it is the single most common misunderstanding the cabinet meets among British residents. Once you are a French tax resident, France taxes your worldwide income, including every pound of interest earned in the United Kingdom. The payment arrives gross not because it is exempt, but because the Franco-British tax treaty gives France — and France alone — the right to tax it. In plain terms, interest from the United Kingdom beneficially owned by a French resident is taxable only in France: Article 12 of the treaty reserves the taxing right to the residence state and leaves nothing to the source state. The British allowances that used to shelter the interest before the move — the Personal Allowance, the starting rate for savings, the Personal Savings Allowance of up to £1,000 — fall away for this income the moment France becomes the taxing state, because those allowances belong to the British tax system and its 6 April to 5 April tax year, not to the French one.

What France charges is a flat-rate levy that surprises many newcomers by its weight: a headline rate of 30 per cent, combining 12.8 per cent income tax and 17.2 per cent social charges. PFU stands for prélèvement forfaitaire unique, the single flat-rate levy, often called the flat tax. It applies automatically unless you make an express election for the progressive scale, and it sits on top of a separate yearly declaration duty for the account itself. The good news is that the system is mechanical and therefore manageable: identify residence, declare the account, declare the interest gross, pay the flat rate or elect the scale, and keep the treaty in reserve for any dispute. The bad news is that each step has a deadline and a price for failure, from the €1,500 fine per undeclared account to social charges wrongly applied to holders of a British S1 healthcare certificate. This article explains, first, where your British savings interest is taxed and at what rate, and secondly, how to declare it correctly and challenge a bill that taxes it twice or taxes it wrongly.

I. Your British savings interest is taxed in France, and the treaty says the United Kingdom must step aside

A. French residence catches your worldwide interest while the treaty blocks British tax

The starting point is whether France regards you as one of its tax residents, because that status drags your worldwide income into the French net. Article 4 B of the General Tax Code treats as French tax residents, in particular, “Les personnes qui ont en France leur foyer ou le lieu de leur séjour principal” — persons who have in France their foyer, the home where the household ordinarily lives, or the place of their main stay. A British citizen who has moved the centre of family life to France, whether under a Withdrawal Agreement residence permit or under a long-stay visa obtained after Brexit, meets that test whatever passport is held and wherever the savings happen to sit. France also looks at where you work and where your centre of economic interests lies, so a household split between the two countries needs to weigh each tie carefully; but for the settled British household with its home in France, residence is rarely in doubt. From that moment, interest credited in London, Manchester or Leeds is French-taxable income in exactly the same way as interest from a French livret, and it must be declared gross, before any foreign charge.

The second half of the mechanism is the treaty, and it works entirely in one direction for savings interest. The France–United Kingdom convention signed in London on 19 June 2008 and published by Decree n° 2010-20 of 7 January 2010 devotes its Article 12 to interest, and paragraph 1 gives France the exclusive right to tax: where the person beneficially entitled to the interest lives in France, the United Kingdom may not tax it at all. The treaty definition of interest is deliberately wide, covering income from claims of every kind, secured or not and with or without a profit-participation clause, including government stock and bond income. Ordinary bank and building-society interest, fixed-term deposit interest and bond coupons all fall squarely inside it, and the treaty expressly carves out only amounts that count as dividends under Article 11. Because France is the residence state, the United Kingdom may not tax the interest at all, which is why it arrives gross; there is no British withholding to reclaim and no British personal allowance to compute, and any British tax that were deducted in error would have to be unwound by reference to the treaty rather than accepted as a credit.

Two practical consequences follow that British newcomers often miss. First, the British allowances described on the official British savings guide — a Personal Savings Allowance of up to £1,000 depending on the tax band, a starting rate for savings of up to £5,000 for savers with low other income, and the exclusion of tax-free accounts such as Individual Savings Accounts (ISAs) from the allowance calculation — belong to the British domestic system and do not reduce the French bill; the full official guide is kept at Tax on savings interest on gov.uk, and it is useful background for understanding what changed at the move, not a shelter that travels with you. An ISA keeps its British shelter but, as our earlier coverage explains, France does not recognise it, so the interest remains declarable in France. Second, the treaty protects only the beneficial owner, the person who genuinely owns the income, and the courts police that condition strictly. In a 2021 decision on the same 2008 convention, the Conseil d’État held that a British collecting society which merely collected royalties in France and passed them to its members could not be regarded as the beneficial owner, finding that the lower court had “inexactement qualifié les faits de l’espèce” — wrongly characterised the facts — before ruling “Les arrêts de la cour administrative d’appel de Versailles des 12 mars et 19 juin 2019 sont annulés” and sending the cases back: Conseil d’État, 5 February 2021, n° 430594 and 432845. The case concerned royalties under Article 13 rather than interest under Article 12, but the lesson travels directly: interest routed through an intermediary, a bare nominee or a vehicle that passes everything on may fail the beneficial-ownership test, while interest paid to you in your own name on your own savings satisfies it without difficulty.

B. The French price tag is 30 per cent flat, unless the progressive scale suits you better

Once the interest is in the French net, the default charge is the prélèvement forfaitaire unique, and its headline figure should be memorised: a global rate of 30 per cent, comprising 12.8 per cent income tax and 17.2 per cent social charges. That breakdown comes from the administration’s own explanatory page at economie.gouv.fr on how the flat levy works, and it splits the bill into its two components. The income-tax component is fixed by Article 200 A of the General Tax Code: “Le taux forfaitaire mentionné au premier alinéa du présent 1 est fixé à 12,8 %”. The social-charges component — the CSG (contribution sociale généralisée), the CRDS (contribution au remboursement de la dette sociale) and the solidarity levy — brings the total to 30 per cent of the gross interest, with no allowance, no deduction for bank charges and no relief for the British personal allowance you may have enjoyed before the move. On £5,000 of British savings interest, the French flat charge is therefore €-equivalent of 30 per cent of the sterling amount converted at the applicable rate: a figure that shocks newcomers precisely because the same interest would have been tax-free in Britain inside the allowances.

The flat rate is the default, not a sentence, because the same Article 200 A offers an express way out: “Par dérogation au 1, sur option expresse du contribuable, l’ensemble des revenus, gains nets, profits, plus-values et créances mentionnés à ce même 1 est retenu dans l’assiette du revenu net global défini à l’article 158. Cette option globale est exercée lors du dépôt de la déclaration prévue à l’article 170, et au plus tard avant l’expiration de la date limite de déclaration.” On an express election by the taxpayer, all of the income otherwise caught by the flat rate is instead brought into the aggregate net income taxed under the progressive scale, and that overall election is made when filing the income return, at the latest by the filing deadline. The election is global — it covers all of the household’s capital income for the year, not just the British interest — and it is worth modelling whenever the household’s marginal rate is low: a retired couple with modest income may pay 0 or 11 per cent on the interest under the scale instead of 12.8 per cent, and the CSG becomes partly deductible the following year, whereas under the flat rate nothing is deductible. The trade-off must be computed across the whole return, including dividends and gains, because the election cannot be sliced interest by interest; a household with large British dividends taxed favourably under the flat rate may sensibly stay with the flat rate for everything.

One mechanism that does not help with British-paid interest, and that causes regular confusion, is the advance levy with its hardship dispensation. Where the payer is established in France, Article 125 A of the General Tax Code subjects French tax residents receiving “intérêts, arrérages et produits de toute nature de fonds d’Etat, obligations, titres participatifs, bons et autres titres de créances, dépôts, cautionnements et comptes courants” — interest and investment income of every kind from government stock, bonds, debt securities, deposits and current accounts — to a levy collected by the French payer, and households whose reference tax income is modest, “inférieur à 25 000 € pour les contribuables célibataires, divorcés ou veufs et à 50 000 € pour les contribuables soumis à une imposition commune”, may claim exemption by sending the payer, “au plus tard le 30 novembre de l’année précédant celle du paiement des revenus”, an attestation on honour under Article 242 quater of the General Tax Code. None of that machinery reaches a high-street bank in Leeds: the levy applies only “lorsque la personne qui assure le paiement de ces revenus est établie en France”, and a British bank is not. British-paid interest therefore suffers no deduction during the year and no 30 November formality; the full choice between the 30 per cent flat rate and the progressive scale is made once, on the French return, with the gross sterling converted to euros.

The social-charges half of the bill deserves a paragraph of its own, because one group of British residents should not be paying it at all. Article L. 136-6 of the Social Security Code makes French tax residents liable to the CSG on capital income assessed on the net amount used for income tax, expressly including “Des revenus de capitaux mobiliers” — investment income — which covers British savings interest just as it covers French interest. But European single-legislation rules, preserved for British S1 holders by the Withdrawal Agreement framework, provide that a person insured in another state is not subject to French social charges on capital income, and the French courts have repeatedly given that principle teeth. In CAA Paris, 3 June 2021, n° 19PA02941, a taxpayer in the line of the de Ruyter case law obtained discharge of social charges on capital income “au titre des années 2012, 2013 et 2014, à concurrence de montants respectifs de 7 382 euros, de 2 304 euros et de 237 453 euros” — a quarter of a million euros for one year alone. The years and the private-insurance facts of that case belong to the pre-Brexit era, but the mechanism is the one a British pensioner holding an S1 healthcare certificate uses today: affiliation evidenced by the S1, charge disputed, discharge claimed. If you hold an S1 and your British interest has been loaded with CSG and CRDS, that line of the assessment should be challenged rather than paid in silence, and our earlier piece on the S1 and social charges walks through the two-gate test in detail.

II. Declare the account and the interest every year, then challenge anything taxed twice or taxed wrongly

A. One form for the account, one entry for the interest, and proof kept for everything

French compliance has two separate limbs and they must not be confused: the account itself is declared on form n° 3916, while the interest is declared as income on the annual return. The account limb is stated by Article 1649 A of the General Tax Code, whose second paragraph provides that individuals domiciled in France “sont tenues de déclarer, en même temps que leur déclaration de revenus ou de résultats, les références des comptes ouverts, détenus, utilisés ou clos à l’étranger” — must declare, together with the income return, the details of accounts opened, held, used or closed abroad. The administration’s English-language guide confirms that foreign accounts are reported together with the yearly income return — see service-public.fr on declaring accounts held abroad. Every British current account, savings account, joint account on which you are a co-holder and account over which you hold a power of attorney needs its own 3916 entry each year it is open, and the duty survives Brexit in full: the United Kingdom is now a third state, and no European tolerance softens the rule. Our companion guide, UK Bank Accounts in France After Brexit: How to Declare Them on Form 3916 and Avoid the €1,500 Fine, inventories every British product account by account; this article deals with the tax on what those accounts earn, so the declaration mechanics are summarised here and developed there.

The income limb is simpler to state and easier to get wrong on the numbers. British interest is declared gross, converted to euros, in the investment-income section of the return with its foreign-origin appendix, and the flat 30 per cent or the progressive scale then applies as described above. Three conversion and completeness points matter. First, use the correct exchange rate and keep the calculation: the administration converts foreign income at the rate applicable to the year of receipt, and a rounded or estimated figure invites a correction with late-payment interest. Second, declare interest you never touched: interest capitalised inside a British savings product, interest credited then swept into another account, and interest on a joint account apportioned to you are all taxable in the year of credit, and the British guide’s note that on joint accounts the interest is split equally between the holders of a joint account unless a different split is evidenced with HMRC is the starting point for the apportionment. Third, Premium Bonds deserve a deliberate choice rather than an assumption: their prizes are not interest in the treaty sense, their British treatment is exempt, and their French characterisation must be settled product by product with the operator’s statements in hand, because declaring them as interest when they are winnings — or omitting them as winnings when the administration reads them as income — are both correctable errors with interest running.

The sanction for skipping the account limb is fixed, personal and confirmed by the courts, which is why the inventory step should come before any computation. Article 1736 IV of the General Tax Code provides: “Les infractions aux dispositions du deuxième alinéa de l’article 1649 A et de l’article 1649 A bis sont passibles d’une amende de 1 500 € par compte ou avance non déclaré”, raised to “10 000 € par compte non déclaré lorsque l’obligation déclarative concerne un Etat ou un territoire qui n’a pas conclu avec la France une convention d’assistance administrative en vue de lutter contre la fraude et l’évasion fiscales permettant l’accès aux renseignements bancaires” — a higher rate aimed at states with no assistance convention with France. The United Kingdom is bound to France by the 2008 convention against double taxation and for the prevention of evasion and fraud, so a British account draws the standard €1,500 per account, while the service-public guide states the same position for the public: a lump-sum fine of €1,500 per undeclared account, rising to €10,000 only where the account sits in a state with no tax cooperation convention with France. Two lines of defence that taxpayers regularly raise have been tested and rejected: in CAA Lyon, 19 September 2024, n° 23LY02010, the court held that the placement of the fine in a section headed for third-party declarants “n’a ni pour objet, ni pour effet de rendre inapplicable l’amende pour défaut de déclaration de compte ouvert, utilisé ou clos à l’étranger prévue au 2. du IV de cet article aux personnes physiques” — neither has the object nor the effect of making the fine inapplicable to individuals — and it threw out the European free-movement-of-capital argument even though the administration could have sought information from the other state’s authorities, ending with “La requête de M. C… est rejetée.” Individuals are liable, the fine stands, and voluntary correction before any inquiry remains the only cheap exit.

B. Challenge double taxation, a wrong rate and wrongly applied social charges

Three distinct errors recur on British-interest assessments, and each has its own remedy. The first is double taxation in the strict sense: British tax deducted or billed on interest that Article 12 reserves to France. The treaty answer is exclusive — France alone taxes — so the remedy runs first against the state that charged in breach of the treaty, with the French return left to tax the gross amount once. Keep every British payslip, P60-style statement, deduction certificate and HMRC letter, because the French administration will ask for proof that the income was declared gross and that any British charge is being unwound at source rather than claimed as a French credit; there is no French credit to claim where France already holds the exclusive right, and manufacturing one on the return creates a second error to defend. Where both states insist, the treaty provides its own escape route beyond domestic appeals: under Article 26 on the mutual agreement procedure, a resident who considers that the measures of one or both states produce taxation contrary to the convention may submit the case to the competent authority, and Article 26 sets the entry conditions — the case must be presented within three years of the first notification of the offending measure — with arbitration available if the authorities cannot agree within two years. That route is slow and formal, which is exactly why it should be opened early, in parallel with domestic steps, rather than discovered after domestic deadlines have expired.

The second error is a wrong French charge: the flat rate applied where the scale election was made, the scale applied where the flat rate was chosen, a dispense wrongly refused on French-paid interest in a mixed portfolio, or social charges loaded onto an S1 holder. The domestic remedy starts with a formal claim to the local tax office. Article R* 190-1 of the Book of Tax Procedures requires it: “Le contribuable qui désire contester tout ou partie d’un impôt qui le concerne doit d’abord adresser une réclamation au service territorial, selon le cas, de la direction générale des finances publiques” — the taxpayer who wishes to challenge all or part of a tax must first send a claim to the local office of the tax administration. The claim must be filed within the limitation period fixed by Article R* 196-1 of the same Book: “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” of collection or payment — 31 December of the second year following the year of the contested charge. And payment need not be made first where the claim says so expressly: Article L. 277 of the Book provides that “Le contribuable qui conteste le bien-fondé ou le montant des impositions mises à sa charge est autorisé, s’il en a expressément formulé la demande dans sa réclamation et précisé le montant ou les bases du dégrèvement auquel il estime avoir droit, à différer le paiement de la partie contestée” — the taxpayer may defer payment of the disputed part on express request stating the amount or basis of the relief claimed. A claim that omits the express deferral request, understates the amount in dispute or misses 31 December of the second year fails on procedure before the treaty is ever read, so the covering letter should plead Article 12, quantify the relief to the euro and invoke Article L. 277 in the same pages.

The third error is subtler and belongs to households, not individuals: the scale election misfiring across a mixed portfolio. Because the Article 200 A election is global for the year, a household that elects the scale to save a few points on modest British interest can accidentally drag large British dividends or gains into the scale at a higher marginal rate, while a household that stays with the flat rate to shelter dividends can overpay on interest that would have borne little or nothing under the scale. The correction is a claim like any other, within the same R* 196-1 deadline, attaching a recomputed return for the year and showing both computations side by side so the office can verify that the election, once corrected, genuinely covers all eligible income. S1 households add one more attachment: the valid S1 certificate and the affiliation evidence for the year, with the CAA Paris discharge figures quoted above as the reason the social-charges line must be isolated and re-examined rather than netted silently into the total. If the office rejects the claim in whole or in part, the rejection opens the appeal to the administrative court within two months, where the treaty text, the case law on beneficial ownership and the social-charges authorities are pleaded in full; and where the dispute turns on what the United Kingdom did or should have done, the mutual-agreement request under Article 26 runs alongside, so that neither state’s clock defeats the other state’s remedy.

Conclusion

British savings interest in French hands follows a short chain with no weak link if each step is taken in order. Residence under Article 4 B pulls the interest into the French return; Article 12 of the 2008 convention reserves it to France and shuts out British tax for the beneficial owner; France charges the 30 per cent flat levy — 12.8 per cent income tax under Article 200 A plus social charges including the CSG under Article L. 136-6 — unless an express global election for the progressive scale made on the return produces a lower bill; the account is declared each year on form 3916 under Article 1649 A on pain of the €1,500 fine under Article 1736, as the Lyon court confirmed against individuals; and any double charge, wrong rate or wrongly applied social charge is challenged first by a reasoned claim to the local office within the 31 December of the second year deadline, with express deferral of the disputed part, then by appeal, with the treaty’s mutual agreement procedure in reserve. The gross payment from Leeds is not a gift from the system; it is France’s exclusive tax base arriving uncollected, and the household that declares it, prices the scale against the flat rate and keeps its treaty proof in a file will pay exactly what the law requires — no more, and no less.

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