You did everything sensibly. Years ago, living in Britain, you opened an Individual Savings Account, an ISA, the tax-efficient savings wrapper that shelters interest, dividends and gains from United Kingdom tax. Then came the move to France: the removal van, the French rental or the Dordogne farmhouse, the registration with the local mairie (town hall) and the first French tax return. And then, one morning, a letter from your British bank or investment platform. It asks you to confirm your residence, warns that since you left the United Kingdom you can no longer pay money into the ISA, and in some cases threatens to restrict or close the account. Panic follows, and with it two opposite mistakes. Some British savers assume the ISA is dead and cash everything in at the worst moment. Others assume the British tax relief travels with them, leave the ISA out of their French return, and discover two years later a demand from the French tax administration, the administration fiscale, with interest for late payment and a very uncomfortable interview about undeclared foreign accounts.

Both mistakes come from the same misunderstanding. Since Brexit you live in France as a third-country national, and France does not recognise the British ISA wrapper. What London exempts, Paris taxes: every pound of interest and every dividend paid inside the ISA becomes taxable in France for the year it arises, at the flat rate on investment income, and the account itself must be declared each year to the French authorities. The good news is that the position is manageable once you understand three things: what you must tell your British provider, what France taxes and at which rate, and how to declare the account and challenge any bill that gets the law wrong. This guide covers all three, with the exact legal texts, the Franco-British double-tax convention (the treaty dividing taxing rights between the two countries) and the court decisions that decide real files.

I. Can I Keep My ISA After Moving to France, and What Does France Tax Each Year

A. Tell Your ISA Provider You Left the United Kingdom: No New Money In, but the Account Stays Open

Start on the British side, because it is the simpler half and the one your provider will enforce first. The official government guidance states the rule plainly on gov.uk for savers moving abroad: once you move abroad and become non-UK resident, you cannot put money into the ISA, apart from a narrow exception for Crown employees working overseas and their spouses or civil partners. The exception is narrow and hiring no one: unless you work directly for the Crown abroad, or you are married to or in a civil partnership with someone who does, every new subscription stops the moment you become non-resident in the United Kingdom. Money already inside keeps its British protection, because the account may stay open with United Kingdom tax relief continuing on the funds and investments it holds And the guidance imposes an immediate duty to tell the ISA provider as soon as United Kingdom residence ends. That notification is not a courtesy. Providers run residence checks, and an ISA fed with fresh subscriptions after departure creates a defective account whose British relief can be clawed back. Write the notification, keep proof of postage or the platform message, and stop any direct debit the same week.

None of that closes the account by itself. Keeping the ISA open while living in France is lawful on the British side, and for many savers it is the right choice: the investments stay put, the British relief continues to apply inside the wrapper, and you can even transfer the ISA to another British provider while non-resident. What changes is everything on the French side. The day you settle in France with the intention to stay, you normally become a French tax resident, and French residence drags your worldwide savings income into French tax, ISA or no ISA. The French test is broader than most British newcomers expect. Article 4 B of the General Tax Code (Code général des impôts) provides: “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 ; b. Celles qui exercent en France une activité professionnelle, salariée ou non, à moins qu’elles ne justifient que cette activité y est exercée à titre accessoire ;” In plain terms, your foyer (the home where your personal life is centred), your principal place of stay, your professional activity or the centre of your economic interests can each, on its own, make you French-resident for tax. Meeting any single one of these tests is enough.

British clients almost always ask the same follow-up question: how many days can I spend in France before I become resident? The honest answer is that day-counting alone does not decide. The Administrative Court of Appeal of Paris made the point in a case about a taxpayer who claimed residence abroad because he could prove 201 days there against 164 in France. The court recalled that “le foyer d’un contribuable célibataire, sans charge de famille, s’entend du lieu où il habite normalement et a le centre de sa vie personnelle, sans qu’il soit tenu compte des séjours effectués temporairement ailleurs en raison des nécessités de la profession ou de circonstances exceptionnelles.” The foyer of a single taxpayer means the place where he normally lives and centres his personal life, ignoring temporary stays elsewhere for work or exceptional events. And the court added: “Le lieu du séjour principal de ce contribuable ne peut déterminer son domicile fiscal que dans l’hypothèse où il ne dispose pas de foyer en France.” The place of principal stay only decides residence where the taxpayer has no foyer in France at all (Administrative Court of Appeal of Paris, 5th chamber, 20 October 2023, No 22PA00816). If your partner, your children, your owned or long-let home and your daily life are in France, you are French-resident from settlement even in a year when travel puts you under 183 days on French soil. Where both countries claim you, the treaty tie-breaker decides, and our companion guide for British taxpayers claimed as resident in both France and the United Kingdom walks through that test and the challenge against double taxation.

Draw the practical consequences in your first French year. First, assume French residence from the date of real settlement and organise the file around that date: the lease or purchase deed, the shipping inventory, school enrolments, the attestation (certificate) from your British provider recording the notification and the balance. Second, do not close the ISA in a hurry to “simplify” matters. Closing a cash ISA and moving the money is neutral, but selling shares or funds inside a stocks-and-shares ISA realises disposals that French law can tax, and a panicked bed-and-breakfast of the whole portfolio in December creates the very bill you wanted to avoid. Third, record the acquisition price of every holding while the British statements are still easy to obtain, because France will want to know your gains when you eventually sell, and reconstructing a ten-year cost history from a closed platform account is miserable work. Fourth, if a provider writes that it will restrict or close non-resident accounts, answer in writing, ask for the contractual clause it relies on, take dated screenshots of every holding, and only then move the assets, so that a later dispute about dates and values is fought on your papers rather than its computer logs.

B. France Taxes the Interest, Dividends and Gains Inside Your ISA Every Year

Here is the central shock, stated bluntly so no one organises their affairs around a comforting myth: France has no equivalent of the ISA, and no provision of French law exempts British ISA income because London exempts it. Once you are French-resident, the interest on a cash ISA and the dividends inside a stocks-and-shares ISA are French-taxable investment income, year by year as they arise, whether or not you withdraw a penny. The charging provision is article 120 of the General Tax Code: “Sont considérés comme revenus au sens du présent article : 1° Les dividendes, intérêts, arrérages et tous autres produits des actions de toute nature et des parts de fondateur des sociétés, compagnies ou entreprises financières, industrielles, commerciales, civiles et généralement quelconques dont le siège social est situé à l’étranger quelle que soit l’époque de leur création ;” Dividends, interest and all similar products of foreign companies are income within the meaning of the article, regardless of when the company was formed. A British bank paying interest on your cash ISA and a British company paying dividends into your investment ISA are both foreign payers for this purpose, and the wrapper around them is invisible to the French statute.

The Franco-British double-tax convention of 19 June 2008, published in France under reference JORFTEXT000021645398, confirms the allocation rather than softening it. For interest, the treaty gives the residence country the exclusive right to tax: under article 12, paragraph 1 of the consolidated Franco-British convention published by the French tax administration, interest arising in one contracting State and beneficially owned by a resident of the other State is taxable only in that other State. Living in France, you are the French-resident beneficial owner of British-source interest, so France alone may tax it, and the United Kingdom, which already grants relief inside the ISA, takes nothing. For dividends the sharing is slightly different: under article 11, paragraph 1 of the same convention, dividends arising in one State and paid to a resident of the other are taxable in that other State, while the source State may also tax them where the recipient is the beneficial owner, subject to a cap of 15 per cent of the gross dividends. In practice the United Kingdom levies no withholding on dividends paid to individuals, so the French bill stands alone here too, and where a foreign withholding has genuinely been suffered, the treaty gives France-side relief capped at the French tax on the same income, a mechanism examined in Part II.

The rate is the flat-rate levy on investment income, the prélèvement forfaitaire unique (single flat-rate levy, universally called the PFU or flat tax). The finance ministry’s official explanation of the PFU presents the headline rate as 30 per cent, comprising 12.8 per cent income tax and 17.2 per cent social levies. The income-tax slice rests on article 200 A of the General Tax Code: “Le taux forfaitaire mentionné au premier alinéa du présent 1 est fixé à 12,8 % ;” The flat rate is set at 12.8 per cent. The social-levies slice rests on contribution law: article L. 136-6 of the Social Security Code (Code de la sécurité sociale) provides that “Les personnes physiques fiscalement domiciliées en France au sens de l’article 4 B du code général des impôts sont assujetties à une contribution sur les revenus du patrimoine assise sur le montant net retenu pour l’établissement de l’impôt sur le revenu,” Individuals resident in France for tax purposes pay a contribution on investment income assessed on the net amount used for income tax, expressly including “c) Des revenus de capitaux mobiliers ;” investment income. One nuance protects you from double deduction at source: the 12.8 per cent collection at source described in article 125 A of the General Tax Code, whose rate is also set by the sentence “Le taux du prélèvement est fixé à 12,8 %.”, applies only where the payer or paying agent is established in France, since the article charges persons receiving interest “lorsque la personne qui assure le paiement de ces revenus est établie en France” (where the person paying the income is established in France). A British ISA provider paying interest in London is outside that collection machinery, so nothing is deducted in Britain and the whole liability is settled on your French return, which is precisely why honest declaration matters so much.

Put figures on it with a simple illustration, converting pounds at the year’s average rate and keeping the arithmetic visible. A cash ISA holding 60,000 pounds earning 4 per cent produces 2,400 pounds of interest in the year. At an illustrative rate of 1.17 euro to the pound, that is about 2,808 euros of French-taxable income. The PFU takes 30 per cent, roughly 842 euros, leaving the saver the interest minus less than a third. A stocks-and-shares ISA paying 3,000 pounds of dividends in the year produces about 3,510 euros of taxable income and roughly 1,053 euros of PFU. These are illustrations, not assessments: exchange rates move, and the progressive-scale election may suit smaller incomes, but the order of magnitude is the point. Every year of silence multiplies the exposure, because each year’s income draws its own assessment, its own late-payment interest and its own questions about the account. Gains work the same way in principle: when you sell a fund or share inside the ISA, French capital-gains rules look through the wrapper and tax the gain realised, which is why the cost records recommended above are worth real money. And if your ISA holds British funds that distribute abnormally large dividends after corporate actions, check the distribution statements line by line, because everything distributed is presumptively taxable in France the year it lands.

II. How to Declare Your ISA in France and Challenge the Bill

A. Declare the Account on Form 3916 and the Income on Forms 2047 and 2042

French compliance has two separate limbs, and confusing them is the classic British error. The first limb is the account itself: every foreign account must be reported each year, even one that earned nothing. Article 1649 A of the General Tax Code states: “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, détenus, utilisés ou clos à l’étranger.” Individuals resident or established in France must declare, with their yearly return, the particulars of accounts opened, held, used or closed abroad. In practice this is the annex form 3916, filed with the main return: one line per account, identifying the British provider, the account number, the dates of opening and where relevant closure, and the nature of the account. A cash ISA, a stocks-and-shares ISA, a Lifetime ISA and even an old ISA you have not touched for a decade each count as an account to list. Closing the ISA during the year does not remove the duty; a closed account is expressly within the list, so the year of closure still carries a 3916 entry recording the closure date.

The second limb is the income: interest and dividends go on the foreign-income schedules, form 2047, whose totals flow into the main return 2042, where the PFU is computed. British landlords living in France already know this pair of forms, and our guide for British landlords declaring United Kingdom rental income on forms 2047 and 2042 explains the mechanics in detail. For ISA income the logic is identical: convert each receipt into euros, enter interest and dividends on the investment-income lines of 2047, carry the totals to 2042, and let the flat rate apply. Keep the provider’s annual tax certificate or consolidated statement stapled, physically or digitally, to your copy of the return, together with the exchange rate source you used. Where the provider’s statement aggregates interest, dividends and equalisation payments, split them before copying figures across, because each category must sit on its own line and a lumped figure invites the inspector to reclassify the whole sum at the least favourable rate.

The price of skipping either limb is severe, and the courts show no tenderness. Where foreign holdings are neither declared nor justified, the administration can deem them a gift and tax them as such: article 755 of the General Tax Code, after listing foreign accounts, capitalisation contracts and crypto holdings, provides that “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 réputés 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 mentionné au tableau III de l’article 777”. Assets on a foreign account whose origin and acquisition the holder cannot justify are deemed, unless he proves otherwise, to be treated as deemed gift wealth taxed at the highest gift-duty rate. The Paris Court of Appeal applied exactly this machinery to a Swiss account whose holder could not justify the funds, upholding gift duty at 60 per cent computed on the 100,001 euros standing on the account at 31 December 2011 (Paris Court of Appeal, Pole 5, Chamber 10, 19 May 2025, RG No 22/15543, confirming the Paris tribunal judiciaire, the ordinary civil court, judgment of 17 May 2022). An ISA is not a hidden Swiss vault, and a saver who declares and justifies has nothing to fear from this weapon, but the decision shows the scale of what non-declaration risks once a file turns adversarial.

Do not count on invisibility either. The Court of Cassation has validated the information pipelines that feed the administration, holding that “l’autorité judiciaire doit communiquer à l’administration des finances toute indication qu’elle peut recueillir, de nature à faire présumer une fraude commise en matière fiscale ou une manoeuvre quelconque ayant eu pour objet ou ayant eu pour résultat de frauder ou de compromettre un impôt,” the courts must pass to the tax authorities any information suggesting tax fraud or any scheme aimed at evading tax, and that “C’est donc à bon droit que la cour d’appel a retenu que la transmission, par le procureur de la République, d’éléments recueillis dans le cadre de l’enquête préliminaire qu’il avait ouverte à la suite de la demande d’entraide internationale émanant des autorités helvétiques, n’était entachée d’aucune irrégularité.” The transmission by the public prosecutor of material gathered in a preliminary investigation opened after a Swiss mutual-assistance request was perfectly regular (Court of Cassation, Commercial Chamber, 14 April 2021, No 19-23.230, ECLI:FR:CCASS:2021:CO00424, concerning nine undeclared foreign accounts and an article 755 assessment). Mutual legal assistance was yesterday’s channel; automatic exchange of financial-account information between the United Kingdom and France is today’s, and British providers report balances and income that the French computer then matches against filed 3916 forms. A missing form beside a reported balance is the cheapest possible trigger for an audit letter. If you discover past omissions, regularise before the administration writes: spontaneous correction normally costs far less than a reassessment built on exchanged data, and your lawyer can frame the late filing as an oversight supported from the start by complete statements.

B. Challenge a Wrong Assessment: Complaint, Treaty Credit and Court Deadlines

Even careful savers receive wrong bills: ISA interest taxed at the progressive scale without the PFU, a treaty credit refused, a year of residence misdated so that pre-arrival British income is swept into French tax, or penalties calculated as though the account had been deliberately concealed. Every one of these can be fought, but only inside the procedural framework, and the framework starts with a written complaint, the réclamation contentieuse (formal tax complaint). Article L. 190 of the Tax Procedure Book (Livre des procédures fiscales) defines the battleground: “Les réclamations relatives aux impôts, contributions, droits, taxes, redevances, soultes et pénalités de toute nature, établis ou recouvrés par les agents de l’administration, relèvent de la juridiction contentieuse lorsqu’elles tendent à obtenir soit la réparation d’erreurs commises dans l’assiette ou le calcul des impositions, soit le bénéfice d’un droit résultant d’une disposition législative ou réglementaire.” Complaints seeking to repair errors in the base or computation of tax, or to obtain the benefit of a statutory right, belong to the contentious jurisdiction. A wrong rate, a denied treaty credit and a misdated residence are all textbook examples: each asks the judge to repair an error in the base or to grant a right flowing from statute or treaty.

Time is the second front, and it is merciless. Article R*. 196-1 of the Tax Procedure Book sets the guillotine: “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,” Complaints must reach the administration by 31 December of the second year following, “a) De la mise en recouvrement du rôle ou de la notification d’un avis de mise en recouvrement ; b) Du versement de l’impôt contesté lorsque cet impôt n’a pas donné lieu à l’établissement d’un rôle ou à la notification d’un avis de mise en recouvrement ;” the collection of the tax roll or the notification of a collection notice, or the payment of the disputed tax where no roll or notice was issued. For ISA income taxed through the yearly return, the clock normally runs from collection of the assessment covering that year. Miss 31 December of year N plus two and the substance of your case no longer matters; file early, by recorded delivery or through your online fiscal account, the espace particulier (personal online tax account), and keep the acknowledgement. If the administration rejects the complaint expressly or stays silent for six months, the dispute moves to the administrative court, the tribunal administratif, within two months of the rejection, where the same exhibits, reorganised around the judge’s questions, do the work a second time.

The treaty’s foreign-tax credit is the most underused weapon in British files, and the one the administration most often mishandles. Where British withholding has genuinely been suffered, for example on certain dividends or on interest that does not qualify for treaty relief, France must grant a credit, but capped: the convention’s elimination article limits the French credit to the amount of French tax attributable to the same income (article 24, paragraph 3, subparagraph a of the consolidated convention linked above). The Conseil d’État, the supreme administrative court, applies exactly this capping technique to treaty credits generally, holding that “Il résulte de ces dispositions que le crédit d’impôt conventionnel correspondant à l’impôt retenu à la source à l’étranger sur les revenus d’origine étrangère visés aux articles 120 à 123 du code général des impôts perçus au cours d’un exercice par une société s’impute sur l’impôt sur les sociétés mis à sa charge au titre de cet exercice, sans qu’il y ait lieu de distinguer selon que cet impôt est dû au taux normal ou au taux réduit, sous la réserve que la déduction n’excède pas le montant de l’impôt français correspondant à ces revenus.” The treaty credit for foreign withholding on articles 120 to 123 income is set against the French tax for the year, whether that tax is due at the normal or the reduced rate, capped at the French tax on that income (Conseil d’État, 9th chamber, 28 March 2018, No 383773). Decided for a company, the mechanics are identical for an individual under the PFU: compute the French flat-rate tax on the gross foreign income, credit the foreign withholding actually and definitively borne, and pay France only the difference. Where the inspector refuses any credit, or credits the wrong amount, or applies the credit to the wrong year, the complaint writes itself around these two texts. And where the administration disputes residence itself, return to the Paris foyer ruling: produce the centred-life evidence, home, family, habitual presence, rather than a bare spreadsheet of days, because the judge weighs the centre of personal life above the calendar.

Run the whole challenge from Britain through a single French lawyer holding a written authority, the pouvoir (power of attorney), to receive documents, request stays of payment and plead. Send that lawyer one organised bundle: the provider’s notification and every annual statement, the 3916 forms and returns as filed, the assessment notices with their envelopes or electronic timestamps, the exchange-rate sources, and every letter from the inspector in chronological order. Ask first for a stay of payment, the sursis de paiement (suspension of collection pending dispute), where the complaint procedure allows it, so that a contested sum does not turn into enforced recovery while the file is pending. Diary separately the complaint deadline, the six-month silence period and the two-month court deadline, because each is fatal if missed and none of them waits for the inspector’s convenience. Never let a file rest on a telephone promise from a helpline: confirm everything in writing, in French, quoting the article numbers above, since only written positions bind the administration and only written exhibits persuade the judge. The through-line of every successful ISA file is the same: provider notified early, account declared yearly, income converted and entered honestly, and any error in the assessment attacked in writing before the guillotine date.

Conclusion

A British ISA does not die when you move to France, but its British tax relief stops at the French border. You must tell your provider the moment you cease to be United Kingdom resident, you may add no new money while non-resident outside the narrow Crown-service exception, and you keep the account open under continuing British relief. From French settlement, France taxes the interest and dividends inside the wrapper each year at the 30 per cent flat rate, 12.8 per cent income tax plus social levies, because articles 120 and 200 A look through the wrapper and the treaty gives France the taxing right over the residence-state income. The account itself is declared yearly on form 3916 alongside the income on forms 2047 and 2042, and the courts punish silence with assessments up to 60 per cent gift duty on unjustified holdings, fed by international information exchange the Court of Cassation has repeatedly blessed. Against a wrong bill, the written complaint before 31 December of the second year, the capped treaty credit and the centred-life residence test give you three solid weapons, provided each deadline is diarised and every figure is proved. Keep the provider’s letters, declare early, compute honestly and challenge in writing: handled that way, the ISA remains a useful British savings pot inside a fully compliant French tax life.

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