You moved to France after Brexit, but your money never fully left Britain. A current account with a high-street bank, a cash ISA you opened years ago, perhaps some Premium Bonds, maybe a savings account you keep “just in case”. Every year the interest ticks up in sterling, and every year the same questions come back: does France tax this interest, do you have to tell the French tax office about accounts held in another country, and what happens if you forgot to do it for years? This guide answers those three questions in order, with the exact legal texts and the court decisions that settle them.

The short version is reassuring on the tax itself and strict on the paperwork. If you genuinely live in France, the France-UK double tax treaty gives France — and only France — the right to tax your UK bank interest. You will not normally pay UK tax on it either. But France taxes it in full: the British ISA shelter stops at the French border, and every account you hold, use or close in the United Kingdom must be declared each year on the foreign-account return known as formulaire n° 3916. Miss that declaration and the fine is automatic; ignore the tax office’s questions for long enough and the balance can legally be treated as an untaxed gift taxed at 60%. Each of these points is explained below, with the remedy that goes with it.

I. Where is my UK savings interest taxed now that I live in France?

A. When France treats you as tax resident and the treaty tie-breaker decides

Everything starts with one concept: the domicile fiscal, the French term for tax residence. French domestic law, at article 4 B of the Code général des impôts (the general tax code), treats you as tax resident in France if you meet any one of three tests: your home or main place of stay is in France, you carry on a professional activity in France, or the centre of your economic interests is in France. Many British settlers meet the first test from the day they move into their French home, even if they still work remotely for a British employer or draw a British pension.

But domestic law is only half the story. Article 4 B adds a decisive sentence that is often overlooked: “Les personnes qui satisfont à l’un au moins des critères fixés aux a à c du présent 1 ne peuvent toutefois pas être considérées comme ayant leur domicile fiscal en France lorsque, par application des conventions internationales relatives aux doubles impositions, elles ne sont pas regardées comme résidentes de France.” In plain terms, even if French internal law calls you resident, the double tax treaty has the last word. If the treaty regards you as a British resident rather than a French one, France must step back.

The treaty that decides this is the convention signed in London on 19 June 2008, published in France by Decree No. 2010-20 of 7 January 2010. Its article 4 provides that a resident of a contracting state means any person who, under that state’s legislation, is liable to tax there by reason of domicile, residence, place of management or any similar criterion. Where both countries claim the same individual — the classic case of a Briton with a house in the Dordogne and a flat in London — paragraph 2 settles the conflict in stages: first the state where the person has a permanent home, and if there is one in each state, then the state with which personal and economic relations are closest, known as the centre of vital interests. Your permanent home comes first, then the centre of your vital interests: family, social life, where you actually spend your time, where your affairs are administered.

The French courts apply this mechanism strictly, and they put the burden of proof on the taxpayer who claims treaty protection. On 11 March 2026 the commercial chamber of the Cour de cassation (the supreme court for civil and commercial matters), in decision No. 25-10.235, recalled that “L’article 4 de la convention […] définit, en son paragraphe 1, le résident d’un Etat contractant comme toute personne qui, en vertu de la législation dudit Etat, est assujettie à l’impôt dans cet Etat en raison de son domicile, de sa résidence, de son siège de direction ou de tout autre critère de nature analogue. Son paragraphe 2 détermine les règles permettant de résoudre le cas dans lequel une personne physique est considérée comme résident de chacun des Etats contractants.” That case concerned the France-Switzerland treaty, but the wording of the residence article is the standard OECD-style clause found in the British treaty too. The taxpayers lost because they could not prove genuine Swiss treaty residence for the year in dispute: to claim a treaty, the court held, taxpayers “doivent démontrer non seulement que les autorités suisses leur attribuent la qualité de résident fiscal en Suisse, mais également qu’ils ont cette qualité au sens de cette convention”. The lesson for British residents of France is practical: keep the evidence of your French centre of life — taxe d’habitation bills, school registrations, French health cover, utility contracts — because if HM Revenue and Customs and the French tax office ever disagree about where you live, documents decide, not assertions.

One more general point before turning to interest itself. Tax treaties define their own scope, and judges read those scope clauses literally. In a February 2026 decision on the France-Canada treaty, No. 23-14.305, the Cour de cassation opened its reasoning with the treaty’s own words: “La présente Convention s’applique aux impôts sur le revenu et sur la fortune perçus pour le compte de chacun des Etats contractants, quel que soit le système de perception.” The France-UK treaty works the same way: it allocates the right to tax each category of income — employment, pensions, dividends, interest — between the two states, and each category has its own article. Savings interest has its own, and it could hardly be clearer.

B. What the France-UK treaty says about interest: it is taxed only where you live

Article 12 of the France-UK treaty is devoted to interest, and its first paragraph removes any doubt: interest arising in one contracting state and paid to a beneficial owner resident in the other state may be taxed only in that other state. If you are treaty-resident in France and you receive interest from a British source, only France may tax it, and the United Kingdom must exempt it. Note the condition attached to this exclusive taxing right: you must be the bénéficiaire effectif, the beneficial owner — the person who genuinely enjoys the income, not a nominee or conduit.

The treaty gives interest a broad meaning covering income from claims of every kind, secured or not, including government securities and bonds, so ordinary bank and savings-account interest falls squarely inside it. Two exceptions matter in practice. First, the residence-only rule does not apply where the interest is effectively connected with a permanent establishment (établissement stable) the recipient maintains in the source state — irrelevant for most private savers. Second, an anti-abuse clause denies the benefit where securing it was a main purpose behind creating or assigning the debt. Parking genuine household savings in Britain is not abuse; routing income through artificial structures might be.

On the French side, domestic law then takes over and taxes that interest in full. Article 120 of the Code général des impôts expressly lists among taxable income “Les dividendes, intérêts, arrérages et tous autres produits des actions de toute nature”, including where the paying company sits abroad, and article 125 A of the same code targets precisely your situation: “Les personnes physiques fiscalement domiciliées en France au sens de l’article 4 B qui bénéficient d’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”. British bank interest received by a French tax resident is therefore part of your worldwide taxable income, declared and taxed under the ordinary rules for investment income, including the single flat-rate levy (prélèvement forfaitaire unique) or, on election, the progressive scale.

This is where the ISA trap lies, and it catches thousands of British settlers. In the United Kingdom an Individual Savings Account shelters interest from UK tax — but that shelter is purely British. The French tax code contains no exemption for income merely because it accrued inside a British ISA wrapper, so articles 120 and 125 A apply to ISA interest exactly as they do to any other British savings interest. The British government’s own guidance, on ISAs for people who move abroad, confirms the cross-border mismatch from the UK side: once you become non-UK resident you may no longer pay money into your ISA, and you must inform your ISA provider as soon as you cease to be UK resident. The consolations are that the ISA itself can stay open with UK tax relief continuing on what it already holds, and that contributions can resume if you return and become UK resident again. So the account survives your move, and Britain continues to shelter it — but France does not, and the interest must appear on your French return every year. The same logic applies to Premium Bond prizes and any other return on British savings: exempt or lightly taxed in Britain does not mean exempt in France.

There is one piece of genuinely good news. Since April 2016 British banks normally pay savings interest gross, without deducting UK tax at source, so most French-resident Britons have no British tax withheld to reclaim through HM Revenue and Customs treaty-relief forms. The treaty simply confirms what already happens in practice: the interest arrives gross from Britain and is taxed once, in France. If in an unusual case British tax has been withheld — for example on certain bonds — keep the certificates, because the treaty relief or a foreign tax credit is claimed with documents, never with explanations alone. Readers with British rental income face a different treaty article and a different mechanism, the foreign tax credit, described in our guide on declaring UK rental income in France.

II. How do I declare UK accounts and challenge penalties if something went wrong?

A. Which forms to file each year: the income return and the 3916 foreign-account return

France separates two duties that British newcomers constantly confuse: declaring the income, and declaring the account itself. The income goes on your annual income return (déclaration des revenus, form 2042) with the foreign-income annex (form 2047) identifying the British source. The account goes on a separate return, formulaire n° 3916, listing every account opened, held, used or closed abroad during the year — current accounts, savings accounts, ISAs, and life-insurance-type contracts. File the income without the 3916, and you are still in breach; file the 3916 without the income, and the breach is reversed. Both must be filed every year, including years when an account earned nothing or was closed mid-year.

The legal basis is article 1649 A of the Code général des impôts, whose wording the Cour de cassation repeated word for word in its September 2025 decision No. 23-10.404: “les personnes physiques, les associations, les sociétés n’ayant pas la forme commerciale, domiciliées ou établies en France, sont tenues de déclarer, en même temps que leur déclaration de revenus ou de résultats, les références des comptes ouverts, utilisés ou clos à l’étranger.” Note the three verbs — opened, used, closed — and the timing — at the same time as the income return. A dormant account you never touched is still “held”; an account you closed in February still counts for that year. British joint accounts, accounts on which you hold a signing authority, and ISAs all fall within the definition of accounts held abroad: when in doubt, declare, because an unnecessary declaration costs nothing and a missing one costs at least 1,500 euros.

Banks and paying agents have mirror duties on their side. Article 242 ter of the Code général des impôts requires those who pay investment income to declare the identity and address of the recipients and the amounts paid, which is how the French tax office cross-checks returns — and, since Brexit, automatic exchange of information with the United Kingdom under the common reporting standard means the French administration increasingly already knows about your British accounts before you declare them. The era when a forgotten Halifax account stayed invisible is over.

The price of forgetting is fixed by law and needs no proof of fraud. The official service-public guidance, in its English-language page on declaring foreign accounts, puts the standard penalty at a flat 1,500 euros per undeclared account. The same page sets a 10,000 euro penalty per account where the account sits in a state that has not signed an anti-fraud tax convention with France — the United Kingdom has signed one, so the ordinary 1,500 euro figure applies to British accounts — and, crucially, an 80% increase of the duties payable on the sums held in the undeclared accounts, which then replaces the flat fine. Where tax was actually avoided, that 80% surcharge on the duties replaces the flat fine and dwarfs it. The statutory basis sits in article 1736 of the Code général des impôts, which also punishes failures linked to the paying-agent reporting duties. Each undeclared account counts separately, and each year counts separately, so three forgotten accounts over four years can mean twelve fines before any tax is even discussed.

A practical filing routine prevents all of this. First, list every British account, including ISAs, joint accounts and any account you closed during the year, and file one 3916 entry per account with the bank’s full details. Second, total all British interest — including ISA interest — convert it to euros at the annual rate, and report it on forms 2042 and 2047 with the treaty position noted. Third, keep the statements and any British tax certificates indefinitely, or at least for the full period the administration can look back, because paper is what wins the disputes described below. Fourth, if you discover an old omission, correct it yourself before the administration finds it: spontaneous regularisation never guarantees immunity, but judges and the administration both treat it very differently from an omission discovered through an audit or an information exchange.

B. How to fix an omission and challenge a fine, a surcharge or a deemed-gift assessment

Not every omission ends in court, and the remedies run from the simplest to the heaviest. Start with the lightest tool: if you spot your own error, file a corrective return as soon as possible and pay the tax due. If the fine has already been notified, the first formal step is the réclamation contentieuse, the written complaint to the tax office that must in most cases precede any court action — set out the facts, attach the statements, identify the exact notices you contest, and keep proof of sending. If the administration maintains the charge, tax disputes go to the tribunal administratif (administrative court), while the heaviest sanction described below can involve the civil courts. Throughout, the strongest arguments are documentary: bank statements proving the modest balance, proof that the income was declared even where the account was not, evidence of good faith such as professional advice followed at the time.

Understand first what you are up against when an omission is discovered by the administration rather than corrected by you. The procedure runs through demandes d’informations — formal requests for information about the origin of the funds — and silence is punished mechanically. The Cour de cassation summarised the chain in its September 2025 decision No. 23-10.404: where the article 1649 A duty has gone unfulfilled, the administration may demand full information on the origin of the funds, and “Selon l’article L. 71 du livre des procédures fiscales, en l’absence de réponse ou à défaut de réponse suffisante aux demandes d’informations ou de justifications prévues à l’article L. 23 C de ce livre dans les délais prévus au même article, la personne est taxée d’office dans les conditions prévues à l’article 755 du code général des impôts.” Automatic assessment — taxation d’office — means the administration assesses without further debate, and article 755 converts the unexplained balance into a deemed gift.

That conversion is the heaviest sanction in this whole area, and its wording must be read carefully: “les avoirs figurant sur un compte ou un contrat d’assurance-vie étranger et dont l’origine et les modalités d’acquisition n’ont pas été justifiées dans le cadre de la procédure prévue à l’article L. 23 C du livre des procédures fiscales sont réputées constituer, jusqu’à preuve contraire, un patrimoine acquis à titre gratuit assujetti, à la date d’expiration des délais prévus au même article L. 23 C, aux droits de mutation à titre gratuit au taux le plus élevé” — see article 755 of the Code général des impôts, as recited by the Cour de cassation in No. 23-10.404. Gift and inheritance tax (droits de mutation à titre gratuit) at the top rate means 60% of the highest balance known to the administration over the previous ten years. Three features save it from being purely confiscatory: it is a rebuttable presumption (“jusqu’à preuve contraire” — until proof to the contrary), so documented savings history defeats it; it applies only after the formal L. 23 C procedure with its deadlines has run; and the extended ten-year recovery period exists precisely because foreign-held assets are harder for the administration to verify. The defence is therefore always the same: answer information requests fully, within the deadline, with bank records tracing the origin of the funds — salary, sale of a British property, documented savings — and the presumption never triggers.

Some taxpayers have tried to attack the whole regime as contrary to European Union free movement of capital, invoking, as recorded in decision No. 23-10.404, the treaty rule that “toutes les restrictions aux mouvements de capitaux entre les États membres et entre les États membres et les pays tiers sont interdites”. The September 2025 decision examined that argument in depth — and rejected it. The Court accepted that the French declaration duty is a restriction in principle, noting that “L’obligation énoncée à l’article 1649 A du code général des impôts […] n’a pas d’équivalent pour les comptes ouverts dans les banques situées en France, lesquels sont déclarés par les établissements bancaires.” But it held the regime justified: the mechanism “poursuit l’objectif constitutionnel de lutte contre la fraude et l’évasion fiscales”, that objective ranks among the overriding reasons of general interest capable of justifying a restriction on capital movements, and given that the information available to national authorities about assets held abroad is “globalement, plus faible que celui dont elles disposent au sujet des avoirs situés sur leur territoire, même en tenant compte de l’existence de mécanismes d’échange d’informations”, the system is apt to achieve its anti-fraud aim. The taxpayer’s appeal was dismissed — “REJETTE le pourvoi”. The message for British savers is blunt: do not build your defence on the hope that a court will strike down the declaration duty itself. Challenge the amount, the facts, the procedure, the good faith, the proportionality of your individual penalty — never the existence of the duty.

Where, then, do real challenges succeed? First, on the facts: an account that was genuinely never held, used or closed by you in the year charged, or a duplicate fine for a single account, can be cancelled on evidence. Second, on good faith and proportionality: a first, small, spontaneously corrected omission with all income duly declared invites reduction arguments that a decade of concealed balances does not. Third, on procedure: the administration must follow the formal steps — proper notice, the L. 23 C request with its sixty-day then thirty-day sequence, assessment within the recovery period — and a skipped step can annul the assessment built on it. Fourth, on the treaty itself: where the administration taxes in France income that the treaty reserves to the United Kingdom — more common with pensions and certain lump sums than with interest — the treaty override described in Part I defeats the assessment outright, as our companion guides on UK rental income and second-home property taxes illustrate for their own treaty articles. Interest is the mirror image — the treaty confirms French taxation — so for savings the fight is about penalties and presumptions, not about the principle of French tax.

Conclusion

British savings in France obey a simple bargain that Brexit did not change. The treaty gives France the exclusive right to tax your British bank interest, so you declare it in France and pay tax once, under articles 120 and 125 A — including the interest inside your ISA, which France does not shelter. In exchange, France demands total transparency through the annual 3916 return for every British account, and punishes opacity with flat fines, an 80% surcharge where tax was at stake, and, for unexplained balances after formal notice, a 60% deemed-gift assessment. The courts have upheld this architecture as a justified weapon against tax fraud, while insisting on proper procedure and rebuttable presumptions. File both returns every year, keep your statements, correct old mistakes before they are found, and answer any information request with documents inside the deadline. Do that, and the British savings you brought with you remain what they should be: a quiet reserve, not a dispute.

Need a quick opinion on your case

If you hold British savings, an ISA or bank accounts and want to check your French tax position, our firm offers a telephone consultation within 48 hours with a lawyer of the firm. Call +33 6 46 60 58 22 or write via our contact page with a short description of your accounts and the years concerned.