You moved to France after Brexit, settled your family, registered with the tax office, and kept your house in Britain as a safety net or a rental. Years later you accept an offer on that British home, and two envelopes land on the doormat in the same season: HM Revenue and Customs wants its share within sixty days of completion, and the French tax office wants the gain on your next income return. British sellers living in France ask the same three questions every week: does France really have the right to tax a house that stands in Manchester or Kent, how is the French bill worked out, and how do you stop the two countries taxing the same pounds twice. The short answers are yes, France taxes the worldwide gains of its residents; the bill is 19% income tax plus 17.2% social charges on the gain after holding-period relief, with a surcharge above 50,000 euros; and the France-United Kingdom treaty of 19 June 2008 gives France a credit for the British tax, capped at the French tax on that gain. This article explains each step in plain English, with the exact legal texts, the official guidance on both sides of the Channel, recent court decisions quoted word for word, and the routes for challenging a wrong assessment.

I. France taxes the sale: are you caught, and what does France take?

A. French tax residence catches your worldwide gains, including the British house

Fiscal domicile, called domicile fiscal, is the trigger. Article 4 B of the French General Tax Code treats you as fiscally domiciled in France if France is your home or your principal place of stay, if you carry on a professional activity here unless it is merely ancillary, or if the centre of your economic interests is here. One criterion is enough. A British citizen who lives year-round in Lyon, works remotely for a French payroll, or simply keeps the family home and the children’s school in France is French tax resident even while keeping a British passport, and French residence makes you taxable on worldwide income and gains. If both countries claim you, the treaty tie-breaker decides; we explained that dual-residence test in our guide to the France-United Kingdom tie-breaker for dual tax residence.

The fact that the house stands in Britain does not take it out of the French net. French domestic law taxes gains on the sale of buildings wherever they stand when the seller is French resident, and the treaty then shares the taxing rights rather than cancelling the French bill. The Conseil d’Etat put the method beyond doubt in a recent treaty case: «Une convention bilatérale conclue en vue d’éviter les doubles impositions ne peut pas, par elle-même, directement servir de base légale à une décision relative à l’imposition et, par suite, il incombe au juge de l’impôt, lorsqu’il est saisi d’une contestation relative à une telle convention, de se placer d’abord au regard de la loi fiscale nationale pour rechercher si, à ce titre, l’imposition contestée a été valablement établie avant de déterminer si cette convention fait ou non obstacle à l’application de la loi fiscale.» That is Conseil d’Etat, 31 May 2022, no. 461519: first French law, then the treaty as a shield. So the order of analysis is fixed: check French residence and the French charge, then use the treaty to remove the double hit.

On the treaty side, the rule for bricks and mortar could hardly be clearer. Article 14, paragraph 1, of the France-United Kingdom convention of 19 June 2008 reserves to the state where the property stands the right to tax gains from its sale, so Britain may tax the disposal under its own non-resident capital gains rules while France, where you live, taxes the same gain as residence state and grants a credit for the British tax. The French tax administration comments this convention in its official doctrine (BOI-INT-CVB-GBR). One warning for readers who left France before selling: Article 150 U, II, 2 degrees, of the General Tax Code grants non-residents an exemption of up to 150,000 euros of net taxable gain on a French home, but only to nationals of the European Union or the European Economic Area. Since Brexit, British nationality alone no longer opens that door, which is one more reason to plan the date of departure and the date of sale together; the mirror situation, a British leaver selling a French home, is covered in our guide to exemption windows and the treaty tail when leaving France.

B. How France works out the bill: gain, reliefs, 19 percent, 17.2 percent and the surcharge

The taxable gain starts from a simple subtraction. Article 150 V of the General Tax Code states: «La plus ou moins-value brute réalisée lors de la cession de biens ou droits mentionnés aux articles 150 U à 150 UC est égale à la différence entre le prix de cession et le prix d’acquisition par le cédant.» Sale price minus acquisition price, both converted into euros for the French return. Add the documented purchase costs, stamp duty land tax paid at the time, agency and legal fees on both transactions, and genuine improvement works supported by invoices from the builders; vague redecoration without paperwork adds nothing. Keep the English completion statement, the original purchase deed, and every invoice, because the French inspector cannot check the Land Registry and will ask you for the file.

Three exemptions can wipe the bill out before any calculation, and each turns on precise facts. First, the main home is fully exempt. Article 150 U, II, 1 degree exempts buildings that constitute the seller’s main residence on the day of sale. For a British home sold while you live in France, that exemption will rarely apply, since your main residence is normally the French one; it matters in the reverse chronology, where you sell the British house just before the French move and it was genuinely your home until completion. The courts read this exemption strictly. In CAA Marseille, 30 December 2021, no. 20MA00667, a seller who claimed to have moved back into her house for the sale failed because electricity bills could only establish a presence «sans justifier que Mme C… l’a occupée elle-même de manière habituelle et effective», while her tax return and her statements to the notary gave a different address, so «le bien en litige ne peut être regardé comme constituant la résidence habituelle et effective de Mme C… veuve A… au moment de sa cession». The lesson for British sellers is blunt: if you claim any residence-based exemption, your tax returns, council tax records, utility consumption, and the address you give the conveyancer must all tell the same story, because the administration cross-checks them.

Second, the first-disposal rule can exempt the gain to the extent you reinvest it. Where you have not owned your main residence, directly or indirectly, during the four years before the sale, the first sale of a dwelling other than your main residence is exempt up to the fraction of the price you reinvest within twenty-four months in buying or building a home you then occupy as your main residence. Miss the deadline or the occupation condition and the exemption is clawed back for the year of the breach. Third, a sale within two years of entering a care home is exempt under strict means conditions. Neither replaces the holding-period relief, which is the workhorse for long-held British property and applies automatically.

The holding-period relief, called abattement pour durée de détention, runs on two different clocks. The official service-public guide to property gains confirms the essentials: no relief for the first five years, then for income tax 6% per year from the sixth to the twenty-first year and 4% for the twenty-second year, giving total exemption from income tax after twenty-two years of ownership; for social charges 1.65% per year from the sixth to the twenty-first year, 1.6% for the twenty-second, then 9% per year from the twenty-third to the thirtieth, giving total exemption after thirty years. The same guide states the rates applied to the gain after relief: income tax at 19% on the gain net of reliefs, plus social charges at 17.2%. The English version of the page adds that form 2048-IMM-SD carries the calculation table and that in practice the notary computes it, which applies to French sales; on a British sale there is no French notary, so you or your adviser perform the same calculation on the return. Above 50,000 euros of taxable gain, Article 1609 nonies G of the General Tax Code adds a surcharge on a sliding scale from 2% to 6%, with smoothing at each threshold, running from «De 60 001 à 100 000 2 % PV» up to «Supérieur à 260 000 6 % PV», the tax being assessed on the total taxable gain.

A worked illustration makes the mechanics concrete. Take a British reader who bought a London flat in 2010 for the equivalent of 230,000 euros and sells it in 2026 for 420,000 euros, with no deductible works for simplicity. The gross gain is 190,000 euros over sixteen years of ownership. For income tax, eleven years of relief at 6% give 66%, so the taxable base is 64,600 euros and the 19% charge is 12,274 euros. For social charges, eleven years at 1.65% give 18.15%, so the base is about 155,515 euros and the 17.2% charge is about 26,749 euros. The taxable gain exceeds 50,000 euros, so the surcharge bites at 2% of 64,600 euros, about 1,292 euros. Total French bill before any treaty credit: roughly 40,315 euros. Every figure in that chain is challengeable, from the acquisition price to the year count, which is why the file of deeds and invoices matters as much as the law.

II. Paying Britain without paying twice, then challenging a wrong bill

A. The British charge, the six-year tail, and the French treaty credit

Britain taxes you as a non-resident seller under its own code, and its deadlines are brutally short. The official GOV.UK guide to tax if you live abroad and sell your UK home warns that even where no tax is due, the seller must still report the disposal to HMRC within 60 days of conveyance. Only the gain since 5 April 2015 is charged, so the valuer’s April 2015 figure or a statutory time-apportionment sets the starting line, and relief is available where you, your spouse or civil partner spent at least ninety days in the home in a tax year, provided you nominate it as your only or main home when reporting. The same guide adds the final-period rule: full relief for the last nine months of ownership where relief was due for any period, thirty-six months for disability or long-term residential care. The annual exempt amount and any unused losses on UK property come off next, the rate follows your UK income band, and where a double taxation treaty removes the British charge you still file the UK return to claim the treaty relief. Miss the sixty-day report and penalties accrue even on a fully relieved sale, so diary the completion date before exchange, not after.

Two treaty traps then decide whether the two bills overlap. First, the six-year tail. The convention preserves each state’s right to tax gains realised by a person who is, or was at any time during the previous six fiscal years, its resident. A reader who left Britain for France three years ago can therefore face a lawful British charge under the tail alongside the French charge, and the treaty resolves the overlap through the credit rather than through exemption. Second, the credit itself. For gains that the situs state may tax, the convention gives the French resident a credit against French tax equal to the tax paid in the United Kingdom, capped at the corresponding French tax, and it is the residence state, France here, that eliminates the double taxation. In practice the British tax paid within the sixty-day window becomes the input for the French foreign-tax-credit computation on the following year’s return, and any excess British tax above the French tax on that gain is simply lost, never refunded by France. That asymmetry makes the British reliefs, the April 2015 rebasing, and the ninety-day nominations financially decisive: every pound removed from the British gain is a pound that does not need a French credit.

The social charges deserve their own warning because they have no British equivalent and no treaty credit. The 17.2% applies in full where you are affiliated to the French social security scheme, which covers most British residents working or retired in France. Readers covered by a British S1 certificate or posted under an A1 may owe only part of the levies, because European case law forbids making a person affiliated in one state contribute to another state’s schemes. The Cour de cassation recalled the principle last year, citing the Court of Justice: a person covered by the coordination regulations «n’est soumise qu’à la législation d’un seul État membre, en sorte que celle-ci, affiliée à un régime de sécurité sociale d’un État membre, ne doit pas contribuer au régime de sécurité sociale d’un autre État membre (CJUE, arrêt du 26 février 2015, De Ruyter, C-623-13, point 35)» (Cass. 2nd civil chamber, 25 September 2025, no. 22-24.634). Since Brexit that coordination runs through the social security protocol of the EU-United Kingdom Trade and Cooperation Agreement rather than the EU regulations directly, so S1 and A1 holders should have their exact levy split confirmed before filing rather than paying 17.2% by default or zero by hope. A final treaty principle helps wherever ownership runs through a company: the Cour de cassation held under the France-Luxembourg convention that fiscally transparent property companies are taxed where the buildings stand and that treaty provisions prevail over domestic law by virtue of Article 55 of the Constitution (Cass. commercial chamber, 2 April 2025, no. 23-14.568), a reminder that wrappers do not move bricks out of the situs state.

B. Declaring, paying, and challenging: deadlines and remedies that actually work

Unlike a French sale, nobody withholds the tax for you. There is no French notary on an English conveyance, no 2048-IMM filed at the mortgage registry, and no deduction from the price by HM Land Registry. You report to HMRC within sixty days of completion and pay the British tax, then declare the worldwide gain on your French income return the following spring, using the foreign-income form alongside the main return, and France assesses the 19%, the 17.2% and any surcharge, minus the treaty credit for the definitively paid British tax. File both sides from the same file: acquisition deed and price, April 2015 valuation or apportionment, improvement invoices, days of occupation for the ninety-day test, the HMRC return and payment receipt, and the euro conversions. If the numbers differ between the two returns, attach a reconciliation note; inconsistent figures across the Channel are the commonest trigger for a French query.

When the French assessment is wrong, the remedies follow a strict order and short clocks. Start with the prior claim to the administration. Article R*196-1 of the Tax Procedure Book requires claims on assessed taxes to reach the administration by 31 December of the second year following collection, payment where there was no assessment, or the event founding the claim, so a 2026 sale declared and assessed in 2027 can normally be challenged until 31 December 2029. The claim must quantify the error, whether it concerns residence, the acquisition price, the relief years, the credit computation, or the social charges, and it suspends nothing, so pay first and argue second to stop late-payment interest. If the administration rejects the claim expressly or stays silent for six months, the dispute moves to the administrative court. Article R421-1 of the Administrative Justice Code provides that the court can only be seized by an action against a decision «dans les deux mois à partir de la notification ou de la publication de la décision attaquée», two months from the rejection, for residents of the Paris region before the Paris administrative court with appeal to the Paris administrative court of appeal. Alongside domestic remedies, the convention opens a mutual agreement procedure where taxation breaches the treaty: the case may be submitted to the competent authority of the residence state within three years of the first notice of the offending measure, or within six years of the end of the fiscal year concerned. The treaty route does not replace the domestic claim, and running both in parallel is standard where the credit or the six-year tail is disputed.

Three practical checks catch most British files before they become disputes. First, verify residence on both sides for the year of sale: a seller who kept a foot in each country should confirm the treaty tie-breaker before choosing where to claim main-home relief, because nominating the British house for HMRC while declaring a French main residence invites both offices to compare notes. Second, verify the holding-period count in years of ownership, not calendar aesthetics: a purchase completed in November 2010 and a sale completed in October 2026 is fifteen full years into the sixteenth, and one missing year of relief moves thousands of euros. Third, verify that the French credit computation uses the British tax definitively borne on that exact gain, after British reliefs and losses, and capped at the French tax computed on the same gain; attaching the HMRC calculation schedule to the French claim turns an argument into proof. For readers in Paris and Ile-de-France, the competent office is the local public finance centre of your domicile for the return and any claim, with the non-resident tax office handling only sellers who have already left; keep the acknowledgement of every filing, because the two-month court clock runs from notification and the administration’s silence is only deemed a rejection after six months.

Conclusion

Selling a British home while living in France is lawful, common, and taxable in both countries by design: Britain taxes the bricks because they stand on its soil, France taxes the gain because you live on hers, and the treaty credit bridges the two. The French bill follows a fixed chain from residence under Article 4 B, through the gain and reliefs of Articles 150 U and 150 V at 19% plus 17.2% with the surcharge above 50,000 euros, to the credit capped at the French tax under the 2008 convention. The British side rewards preparation even more, since the April 2015 starting line, the ninety-day nominations, the final nine months, and the sixty-day filing all shrink the gain before any credit is needed. Build the file at exchange, not at assessment: deeds, valuations, invoices, occupation evidence, and the HMRC computation. And where the assessment misstates residence, miscounts the years, or short-changes the credit, claim within the R*196-1 deadline, go to the administrative court within two months of rejection, and invoke the mutual agreement procedure where the treaty itself is breached. Ordered this way, the sale funds your French life instead of funding two treasuries for the same gain.