When you move from London, Manchester or Edinburgh to Paris, Lyon or the Dordogne, one question follows you across the Channel with your savings: does my ISA stay tax-free? The short answer, which surprises many British newcomers, is no. A Cash ISA, a Stocks and Shares ISA, a Lifetime ISA and even Premium Bonds keep their British tax shelter only while the United Kingdom taxes you. Once you are fiscally domiciled in France, France taxes your worldwide investment income, and the Franco-British double tax treaty of 19 June 2008 decides which country gives way, by how much, and by which method. This guide explains, for a British reader with no French legal training, why the wrapper fails, how each product is taxed, which forms to file, which fines to avoid, and how to challenge a wrong bill from Paris or elsewhere in France. Every French term is explained at first use.<\/p>\n
French domestic law starts with a wide net. Article 4 B of the French Tax Code (Code g\u00e9n\u00e9ral des imp\u00f4ts<\/em>) provides that “Sont consid\u00e9r\u00e9es 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 s\u00e9jour principal” \u2014 in plain English, anyone whose home (foyer<\/em>) or principal place of stay is in France is treated as fiscally domiciled here: Article 4 B, Code g\u00e9n\u00e9ral des imp\u00f4ts (L\u00e9gifrance)<\/a>. Two further tests can also catch you: carrying on a professional activity in France, or having the centre of your economic interests here. Meeting any one of the three is enough, and the same article adds that treaty tie-breaker rules can still deprive France of residence where a double tax convention allocates it elsewhere.<\/p>\n In practice, a British retiree renting a flat in the 7th arrondissement of Paris, a remote worker whose family home is in Bordeaux, or a seconded executive whose children attend school in France will normally meet the foyer test from the year of arrival. From that point, Article 4 A makes them liable to French income tax on worldwide income, including interest and dividends that the United Kingdom would have left alone inside an ISA. The French avis d’imposition<\/em> (tax assessment notice) will therefore expect to see those amounts, converted into euros at the annual rate, even where no British tax was charged.<\/p>\n The treaty does not rescue the wrapper. The France\u2013United Kingdom Convention signed in London on 19 June 2008, in force since 18 December 2009 and effective in France from 1 January 2010, allocates taxing rights between the two states but nowhere recognises the ISA as an exempt vehicle: 2008 UK\u2013France Double Taxation Convention (GOV.UK)<\/a>. Its residence article follows the familiar OECD pattern: where both states claim you under domestic law, the treaty tie-breaker looks first to a permanent home, then to the centre of vital interests, then to habitual abode, then to nationality, and finally to mutual agreement. A Briton who keeps a London flat but lives year-round with family in France will generally lose that tie-break to France, because the permanent home available to them and the closer personal and economic relations point here. Our companion guide to your first French tax return after the move (forms 2042, 2047 and 3916)<\/a> walks through that residence analysis step by step.<\/p>\n The British side of the story is worth stating precisely, because the misunderstanding starts there. The United Kingdom government presents ISAs as a way to save free of United Kingdom tax (Individual Savings Accounts: overview (GOV.UK)<\/a>). That promise is a creature of British domestic law \u2014 exemption from United Kingdom income tax and capital gains tax on returns inside the wrapper \u2014 and it binds His Majesty’s Revenue and Customs, not the French Direction g\u00e9n\u00e9rale des finances publiques<\/em>. France never signed an agreement exempting ISA returns, and Article 120 of the French Tax Code expressly pulls foreign-source investment income into the French base, including “Les dividendes, int\u00e9r\u00eats, arr\u00e9rages et tous autres produits des actions de toute nature” from companies whose registered office sits abroad: Article 120, Code g\u00e9n\u00e9ral des imp\u00f4ts (L\u00e9gifrance)<\/a>. The same article reaches government stock and foreign bonds through “Les int\u00e9r\u00eats, arr\u00e9rages, et tous autres produits de rentes, obligations et autres effets publics des gouvernements \u00e9trangers”. Cash ISA interest, ISA dividends and most bond fund distributions therefore fall squarely inside French taxable income once you live here.<\/p>\n A useful illustration of treaty method comes from the French supreme court for civil and commercial matters, the Cour de cassation<\/em>. In a trust and treaty-scope dispute decided on 11 February 2026 (appeal no. 23-14.305), the court recalled the standard formula that “La pr\u00e9sente Convention s’applique aux imp\u00f4ts sur le revenu et sur la fortune per\u00e7us pour le compte de chacun des Etats contractants, quel que soit le syst\u00e8me de perception.”: Cour de cassation, chambre commerciale, 11 f\u00e9vrier 2026, n\u00b0 23-14.305<\/a>. The wording there concerned the Franco-Canadian convention, but the reasoning method is identical for the Franco-British text: the court reads the treaty article by article, checks which tax each state was entitled to levy, and then applies the elimination-of-double-taxation article. For ISA income, that means asking separately for interest, for dividends and for any other gain which article governs, and then applying the French credit method rather than assuming an exemption.<\/p>\n Two practical consequences follow before a single euro of product detail. First, you should not close everything in panic the week you arrive, but you should stop assuming the wrapper protects you and budget for French tax from the year you meet the foyer test, pro rata where the move happens mid-year. Second, keep every British voucher, consolidated tax certificate and NS&I prize statement from the year of arrival: France will ask for gross amounts, dates of payment and any foreign tax actually withheld, and reconstructing twelve months of ISA statements under time pressure is how errors begin.<\/p>\n Start with the simplest product, the Cash ISA. Interest paid inside a Cash ISA is exempt in the United Kingdom, but in France it is ordinary taxable interest. The treaty rule for interest is unusually clean. Article 12, paragraph 1 of the 2008 Convention gives the exclusive right to tax interest to the state where the beneficial owner is resident (Article 12, UK\u2013France Convention (GOV.UK)<\/a>). In everyday terms, where you are resident in France and beneficially own British-source interest, only France may tax it. The United Kingdom should not withhold, and in practice British banks and building societies pay Cash ISA interest gross. France then taxes it under domestic law: Article 125 A of the Tax Code imposes the withholding mechanics for interest paid through a French paying agent, and states the rate rule plainly \u2014 “Le taux du pr\u00e9l\u00e8vement est fix\u00e9 \u00e0 12,8 %.” (Article 125 A, Code g\u00e9n\u00e9ral des imp\u00f4ts (L\u00e9gifrance)<\/a>). For interest paid directly by a British institution with no French intermediary, no French pr\u00e9l\u00e8vement<\/em> (advance levy) is taken at source; the 12.8 per cent instead arrives as part of your final French income tax bill under the flat-tax system described below, plus 17.2 per cent of social levies (pr\u00e9l\u00e8vements sociaux<\/em>) where you are affiliated to the French social security system. Cash ISA interest is therefore fully declarable, fully taxable in France, and credit-free because there is no British tax to credit.<\/p>\n Stocks and Shares ISA dividends are slightly more layered. British domestic law currently pays dividends without withholding, so most investors see no British tax deducted. The treaty nevertheless reserves a taxing right to the source state: Article 11 provides that dividends arising in one state and paid to a resident of the other may be taxed in that other state, and may also be taxed in the source state, but caps the source-state tax at 15 per cent of the gross dividend where the recipient is the beneficial owner (Article 11, UK\u2013France Convention (GOV.UK)<\/a>). For a French-resident holder of a Stocks and Shares ISA invested in United Kingdom equities, France taxes the gross dividend and, if any British withholding had been levied up to the 15 per cent ceiling, would grant a credit under Article 24 within French limits. Where, as is usual, no British withholding was levied, France taxes the full dividend with no credit to give. The position changes for an ISA holding American or European equities through a British platform: the United States, for example, typically withholds 15 per cent on dividends paid to a French resident claiming treaty relief via a W-8BEN, and France then grants a credit equal to the foreign tax within the limit of the French tax attributable to that income, under the Article 24 mechanics explained in Part II. Keep the American 1042-S or the broker withholding statement: without proof of foreign tax effectively and definitively borne, the French inspector will refuse the credit.<\/p>\n Lifetime ISAs add a British bonus that France ignores. The 25 per cent government top-up \u2014 up to \u00a31,000 per year on \u00a34,000 of subscriptions \u2014 is a British budgetary incentive, not a treaty-exempt capital sum in French eyes. If you subscribed before the move and the bonus was already vested, France does not retroactively tax the past; but interest and dividends subsequently generated by the Lifetime ISA balance are taxed exactly like any other ISA return, and any withdrawal itself follows the nature of the underlying gain rather than enjoying a French exemption. Do not confuse the Lifetime ISA with the French Plan d’\u00e9pargne en actions<\/em> (PEA, a French share-savings plan with its own holding conditions): the two wrappers are strangers to each other, and holding one does not satisfy the conditions of the other.<\/p>\n Premium Bonds deserve their own paragraph because clients consistently misread them. National Savings and Investments, the state-owned savings bank, advertises Premium Bonds as paying prizes free of United Kingdom tax, from \u00a325 up to \u00a31 million: Premium Bonds (NS&I)<\/a>. That advertisement speaks of British tax. In France, monthly prizes drawn on bonds you hold as a French resident are not covered by any treaty exemption for gambling or lottery, and the French administration treats them as taxable movable income within Article 120 \u2014 the same family as “lots et primes de remboursement” (prize draws and redemption premiums) \u2014 to be declared for the year of receipt and taxed at the flat-tax rate or, on global option, at the progressive scale, plus social levies. No British tax is withheld on prizes, so again there is no foreign credit; the prize is simply added to your French base. Small prizes of \u00a325 are taxable in exactly the same way as a \u00a31,000 win: the threshold that matters is not the size of the prize but your French residence on the date of the draw. Keep the NS&I prize notifications and the annual statement, because the Service des imp\u00f4ts des particuliers<\/em> (SIP, the local personal tax office) cannot verify them automatically and will ask you for the schedule.<\/p>\n A final product warning concerns funds labelled “accumulating” or “roll-up” inside a Stocks and Shares ISA. France generally taxes the distributed amount for distributing share classes, but for accumulating funds it may tax annually the share of interest and income capitalised within the fund under the bond-fund transparency rules, with the balance taxed as a capital gain on disposal. The detailed fund-by-fund treatment exceeds this guide, but the lesson is constant: the ISA label changes nothing, and each underlying stream \u2014 interest, dividend, prize, capitalised income, eventual gain \u2014 must be characterised under French domestic law and then run through the treaty article that matches its nature. Where the ISA provider’s consolidated certificate lumps everything as a single ISA figure, ask for the analytical breakdown before filing; inspectors in Paris and the large provincial SIPs now routinely request it.<\/p>\n French filing starts with Article 170 of the Tax Code, which requires every person liable to income tax to file a detailed return of income, gains, household composition and every element needed to compute the tax: Article 170, Code g\u00e9n\u00e9ral des imp\u00f4ts (L\u00e9gifrance)<\/a>. For a British newcomer this means three coordinated forms. Form 2042 (d\u00e9claration des revenus<\/em>) carries the totals. Form 2047 (revenus encaiss\u00e9s \u00e0 l’\u00e9tranger<\/em>, income received abroad) carries the analytical detail: country by country, nature by nature, gross amount, foreign tax withheld, and credit claimed. Form 3916 (d\u00e9claration des comptes ouverts \u00e0 l’\u00e9tranger<\/em>) identifies every foreign account \u2014 and each ISA counts as an account, even where the provider calls it a wrapper, a plan or a bond holding.<\/p>\n The account-declaration duty is strict and personal. Article 1649 A, second paragraph, states: “Les personnes physiques, les associations, les soci\u00e9t\u00e9s n’ayant pas la forme commerciale, domicili\u00e9es ou \u00e9tablies en France, sont tenues de d\u00e9clarer, en m\u00eame temps que leur d\u00e9claration de revenus ou de r\u00e9sultats, les r\u00e9f\u00e9rences des comptes ouverts, d\u00e9tenus, utilis\u00e9s ou clos \u00e0 l’\u00e9tranger.” (Article 1649 A, Code g\u00e9n\u00e9ral des imp\u00f4ts (L\u00e9gifrance)<\/a>). Concretely: one Cash ISA with Halifax, one Stocks and Shares ISA with Vanguard UK and one NS&I Premium Bond holding mean three 3916 entries, each with the institution’s name and address, the account number, and the opening date \u2014 and a closing entry in the year you shut one. The official form and notice are published by the tax administration here: Formulaire n\u00b0 3916 (impots.gouv.fr)<\/a>, with the general guidance in English here: Must you declare accounts opened abroad? (Service Public, English)<\/a>. Jointly held ISAs are not joint in Britain \u2014 ISAs are individual by statute \u2014 so each spouse declares their own; Premium Bonds held for minor children are declared by the parents with the child’s identification.<\/p>\n The sanction for forgetting is automatic and per account. Article 1736, paragraph IV provides: “Les infractions aux dispositions du deuxi\u00e8me alin\u00e9a de l’article 1649 A et de l’article 1649 A bis sont passibles d’une amende de 1 500 \u20ac par compte ou avance non d\u00e9clar\u00e9.” (Article 1736, Code g\u00e9n\u00e9ral des imp\u00f4ts (L\u00e9gifrance)<\/a>). The same paragraph raises the fine to 10,000 euros per account only where the account sits in a state without administrative assistance with France \u2014 not the British case, since the United Kingdom exchanges banking information \u2014 but 1,500 euros per ISA per year still accumulates quickly across a Cash ISA, a Stocks and Shares ISA and Premium Bonds. Beyond the fine, the third paragraph of Article 1649 A creates a presumption that sums transferred abroad or from abroad through undeclared accounts constitute taxable income unless you prove otherwise, which reverses the burden of proof in a way few British taxpayers expect. Late regularisation reduces but does not erase the risk, as the case law below shows.<\/p>\n The income declaration itself follows a fixed order. First, convert each gross receipt into euros and enter interest in the 2TR\/2BH boxes series, dividends in the 2DC\/2FU series, and Premium Bond prizes alongside other movable income, with the analytical detail on form 2047 showing the United Kingdom as source country and the treaty article relied upon. Second, compute the levy. Since 2018, investment income is subject by default to the pr\u00e9l\u00e8vement forfaitaire unique<\/em> (PFU, single flat levy) of 30 per cent, comprising 12.8 per cent income tax and 17.2 per cent social levies: Article 200 A, Code g\u00e9n\u00e9ral des imp\u00f4ts (L\u00e9gifrance)<\/a>. Article 125 A operates the 12.8 per cent as an advance where a French paying agent is involved; for British-paid ISA income with no French intermediary, the 12.8 per cent is simply assessed on the return rather than withheld upstream. Third, decide whether the flat 30 per cent or the progressive scale (bar\u00e8me progressif<\/em>) suits you: Article 200 A allows a global, express, irrevocable-for-the-year option to tax all eligible investment income and gains at the progressive scale, exercised when filing. The scale brings the 40 per cent dividend allowance (abattement de 40 %<\/em>) for qualifying dividends and the deductibility of part of the contribution sociale g\u00e9n\u00e9ralis\u00e9e<\/em> (CSG, the main social levy), but it also pushes total income into a higher marginal band and forfeits the flat rate. As a rule of thumb, modest ISA returns alongside a French salary often favour the flat levy, while large United Kingdom dividends received by a household with little other income can favour the scale \u2014 but the comparison must be computed household by household, year by year, before ticking the 2OP box, because the option covers every eligible receipt of the year, not the ISA alone.<\/p>\n Fourth, claim the treaty credit exactly where the treaty allows it. The French elimination method in Article 24 of the Convention gives a French resident a credit against French tax for the treaty-covered foreign tax, within the conditions and ceilings stated in that article (Article 24, UK\u2013France Convention (GOV.UK)<\/a>). For dividends within Article 11, the credit equals the British tax paid within the 15 per cent ceiling, capped at the French tax attributable to the same income; for interest within Article 12, there is normally no British tax and therefore no credit. Attach every withholding certificate, claim the credit on form 2047 in the treaty-credit columns rather than as a deduction from gross, and never deduct foreign tax from the declared gross: deducting instead of crediting is the single most frequent cause of reassessment on British files, because it understates both gross and the French tax base. Our analysis of the 25 per cent pension lump sum France still taxes<\/a> shows the same credit-versus-deduction mechanics on another class of British receipts.<\/p>\n Two administrative points close the method. Where your reference tax income (revenu fiscal de r\u00e9f\u00e9rence<\/em>) for the year before last falls below 25,000 euros for a single person or 50,000 euros for a jointly taxed household, you may request exemption from the 12.8 per cent advance on French-paid interest by filing the affidavit (attestation sur l’honneur<\/em>) with the French payer before 30 November of the preceding year \u2014 a useful cash-flow step where a French bank tops up a Livret A alongside the ISA, though it changes nothing for British-paid ISA income. And where you arrive mid-year, split the return: British-source income received before the move, while you were still United Kingdom resident, is generally outside the French return, while income received after the foyer moved is declarable even if it accrued earlier. Date of receipt, not date of accrual, governs \u2014 so a dividend declared in March but paid in July after your June arrival falls inside the French return.<\/p>\n Controls on British files typically start with a mismatch: the international exchange of Banking information sends the French administration the ISA balances, while the 3916 or 2047 lines are missing or inconsistent. The administration then issues a proposition de rectification<\/em> (proposed reassessment) or, for missing 3916 entries, a flat fine notification. Understanding the order of battle matters, because each paper has its own deadline and its own judge.<\/p>\n Start with the 3916 fine, the most common shock. The Lyon Administrative Court of Appeal (Cour administrative d’appel de Lyon<\/em>), second chamber, 19 September 2024, no. 23LY02010, heard a taxpayer holding five undeclared Swiss accounts who had regularised late in 2017 and argued, among other points, that the fines restricted the free movement of capital and were disproportionate where the administration could have obtained information from Switzerland: CAA Lyon, 2e ch., 19 sept. 2024, n\u00b0 23LY02010 (L\u00e9gifrance)<\/a>. The court rehearsed the duty in these terms: “Les personnes physiques (…) domicili\u00e9es ou \u00e9tablies en France, sont tenues de d\u00e9clarer, en m\u00eame temps que leur d\u00e9claration de revenus ou de r\u00e9sultats, les r\u00e9f\u00e9rences des comptes ouverts, utilis\u00e9s ou clos \u00e0 l’\u00e9tranger.” The lesson for ISA holders is direct: late disclosure does not retroactively erase the breach for the years when the 3916 was missing, and proportionality arguments succeed only with concrete proof that the penalty exceeds what anti-evasion enforcement requires. Practically, where you discover missing ISA or Premium Bond 3916 entries, file a corrective return immediately, pay the fine under protest where demanded, and plead spontaneous regularisation and good faith for a discretionary reduction (remise gracieuse<\/em>) rather than expecting annulment as of right. Keep the sent receipts from the online filing portal (messagerie s\u00e9curis\u00e9e<\/em>), because proof of the date of spontaneous disclosure is routinely decisive.<\/p>\nB. Cash ISA interest, stocks-and-shares dividends and Premium Bond prizes: what France taxes and what the treaty allows<\/h3>\n
II. Declaring each product without triggering a fine, and fighting back when the bill is wrong<\/h2>\n
A. Forms 2042, 2047 and 3916, the 12.8 per cent charge and the flat-tax choice: a declaration method that survives control<\/h3>\n
B. Fines, presumptions and wrong treaty credits: how to challenge a reassessment from Paris and the Ile-de-France<\/h3>\n