Since Brexit, British citizens living in France are third-country nationals. A Withdrawal Agreement residence permit (titre de séjour accord de retrait du Royaume-Uni) protects your right to stay, but it does not give you a French passport, a vote in national elections, or freedom from the paperwork of renewals. For many Britons who have made France their home, the next logical step is naturalisation par décret — naturalisation by government decree — which makes you French while letting you stay British. The route is open, it is well used, and it ends with two passports in the same drawer. It is also demanding: five years of settled life as a rule, French tested at an exacting level, a personal interview at the préfecture (the local office of the French state), and an administration that can say no, or make you wait. This guide explains who can apply, what dual nationality really means for a Briton, how the assimilation test works in practice, and — because refusals and postponements (ajournements) are common — how to challenge an unfavourable decision, step by step, with the court rulings that show what judges actually accept.

I. Can a Brit Become French After Brexit and Keep the British Passport?

The short answer is yes on both counts. Nothing in French law reserves naturalisation to European Union citizens, and neither London nor Paris forces you to choose between the two nationalities. The longer answer is that each side of the Channel has its own rules, and you must satisfy both. France decides whether you become French; Britain decides whether you remain British. Happily, both answers point the same way, provided you prepare the file properly.

A. Who Can Apply for Naturalisation by Decree: Five Years, Shorter Routes and Where Your Life Must Be Centred

Naturalisation by decree is exactly what its name says: a favour of the state granted by decree at the foreigner’s request. Article 21-15 of the Civil Code (Code civil) puts it in one sentence: “Hors le cas prévu à l’article 21-14-1 , l’acquisition de la nationalité française par décision de l’autorité publique résulte d’une naturalisation accordée par décret à la demande de l’étranger.” Three features follow from that sentence. First, it is a request you make, not a right you claim: the administration keeps a wide discretion (pouvoir discrétionnaire). Second, it is granted by decree, signed at the highest level of the state. Third, it concerns foreigners as such — and since 1 January 2021, that includes British citizens, who lost EU citizenship with Brexit and now apply on exactly the same footing as Americans, Australians or Canadians.

The headline condition is time. Article 21-17 of the Civil Code provides: “Sous réserve des exceptions prévues aux articles 21-18 , 21-19 et 21-20 , la naturalisation ne peut être accordée qu’à l’étranger justifiant d’une résidence habituelle en France pendant les cinq années qui précèdent le dépôt de la demande.” Five years of habitual residence (résidence habituelle) immediately before the application: that is the standard clock for a Briton who moved to the Dordogne, Brittany or Paris after the referendum and has lived there ever since. Short absences for holidays or family visits do not break the clock, but the centre of your life must have been France for those five years, and you must hold a valid residence permit (titre de séjour) when you apply — for most Britons, the Withdrawal Agreement card or a standard carte de séjour.

The clock can run faster in several cases that matter to British applicants. Article 21-18 of the Civil Code reduces the qualifying period (stage) to two years: “Le stage mentionné à l’article 21-17 est réduit à deux ans : 1° Pour l’étranger qui a accompli avec succès deux années d’études supérieures en vue d’acquérir un diplôme délivré par une université ou un établissement d’enseignement supérieur français ; 2° Pour celui qui a rendu ou qui peut rendre par ses capacités et ses talents des services importants à la France ; 3° Pour l’étranger qui présente un parcours exceptionnel d’intégration, apprécié au regard des activités menées ou des actions accomplies dans les domaines civique, scientifique, économique, culturel ou sportif.” A British graduate of a French university, a researcher recruited by a French laboratory, or a Briton with a genuinely exceptional civic or cultural record in France can therefore apply after two years. Article 21-19 goes further and removes the qualifying period entirely for narrow categories, including foreigners who have served in the French army and recognised refugees (réfugiés statutaires): the official service-public.fr guide confirms that refugees and several other narrow profiles face no minimum residence period at all, while French-university graduates and comparable cases wait only two years. Check the current service-public.fr page “Naturalisation française par décret”, verified 16 July 2026, before you count your years, because the exemptions are read strictly and the prefecture will not credit a year you cannot prove with tax notices (avis d’imposition), pay slips and rent receipts.

Time alone is never enough: your life must be centred in France. Article 21-16 states the rule bluntly: “Nul ne peut être naturalisé s’il n’a en France sa résidence au moment de la signature du décret de naturalisation.” In practice the administration reads “residence” as the centre of your material interests and family ties (centre des intérêts matériels et des liens familiaux). The classic refusal in British files is the split household: you live near Bergerac while your spouse and children stayed in Kent, or your professional life — directorships, self-employment, tax residence — remained in Britain. The official guidance warns openly that if your husband, wife or children live abroad, French nationality can be refused even after many years of your own presence. Before applying, align the visible facts: bring the family, move the tax residence, and make sure your French tax returns show France as the home base. A Briton who spends four months a year in a second home in France and the rest in Surrey is a visitor with a beloved holiday house, not a candidate for naturalisation.

Two practical points complete the picture. The application costs 255 euros, paid with an online fiscal stamp (timbre fiscal), and the file is now lodged online through the ANEF portal (Administration numérique pour les étrangers en France) with originals produced later at the interview. Both spouses must file separate applications if both want to become French. And majority matters: you must be 18, though you may lodge the file from 17, and a minor child who has lived in France with a newly naturalised parent for five years can be swept into the parent’s decree.

B. Keeping Both Passports: What London and Paris Each Say, the Marriage Route and the Children

The question every British applicant asks first is whether becoming French means ceasing to be British. On the British side the answer is a clear no. The official British government guide on dual citizenship confirms that the United Kingdom allows dual nationality, so a British citizen may also become a citizen of other countries. There is no separate application for dual status: you apply for the foreign citizenship and keep your British citizenship, while checking with the other country that it too accepts dual nationality (gov.uk guide to dual citizenship). No declaration, no permission, no fee in London: you apply in France, and Britain simply continues to treat you as British. The same page adds the honest warning that many countries do not accept dual nationality and tells readers to check with the country’s embassy — and that check, for France, comes back positive.

On the French side, France has accepted dual nationality (double nationalité or plurinationalité) for decades. No provision of the Civil Code requires a naturalised Briton to renounce (répudier) British citizenship, and the naturalisation decree does not ask for any renunciation certificate. You will therefore hold two passports, two sets of civic rights, and — this is the part to organise rather than fear — two potential tax and military administrations interested in you. National service (service national) is suspended in France and does not trouble British applicants in practice; taxation is governed by the France–United Kingdom double tax treaty, and becoming French does not by itself change your tax residence, which still depends on where your home, work and centre of interests lie. The genuine practical effects are positive: as a French citizen you recover the EU citizenship Brexit took away — free movement across the Union, the right to vote in all French elections including parliamentary and presidential ones, and unrestricted access to French public employment (fonction publique).

A distinct fast track exists for Britons married to a French citizen: acquisition by declaration after marriage (déclaration à raison du mariage). Article 21-2 of the Civil Code provides: ” L’étranger ou apatride qui contracte mariage avec un conjoint de nationalité française peut, après un délai de quatre ans à compter du mariage, acquérir la nationalité française par déclaration à condition qu’à la date de cette déclaration la communauté de vie tant affective que matérielle n’ait pas cessé entre les époux depuis le mariage et que le conjoint français ait conservé sa nationalité “ — four years of marriage with an unbroken shared life, extended to five years if you cannot show three years of uninterrupted regular residence in France or if your French spouse only recently registered as French while living abroad. Note the vocabulary: this is a declaration you subscribe, not a favour you request, so the logic is reversed — you become French unless the state objects. But the state can object. Article 21-4 allows the Government to oppose the acquisition by decree in the Council of State (décret en Conseil d’État) on grounds of unworthiness or failed assimilation: “Le Gouvernement peut s’opposer par décret en Conseil d’Etat, pour indignité ou défaut d’assimilation, autre que linguistique, à l’acquisition de la nationalité française par le conjoint étranger dans un délai de deux ans à compter de la date du récépissé prévu au deuxième alinéa de l’article 26”. Opposition must come within two years of your receipt (récépissé), and the decided cases show exactly what “failed assimilation” means — a married British applicant whose prefecture interviews reveal rejection of Republican values can be blocked just as a decree applicant can, a point developed below.

Children deserve their own paragraph because Brexit made their position sharper. A child born in France to British parents does not automatically become French at birth; but a child born in France who has lived there for at least five years since the age of 11 becomes French automatically at 18 (acquisition de plein droit), and can claim French nationality from 13 to 18 by declaration with parental consent. Meanwhile, the minor child of a newly naturalised British parent can be included in the parent’s decree if the child has lived with that parent in France for the previous five years. British parents should therefore time the family strategy: your naturalisation can carry young children with it, while teenagers born and schooled in France have their own route. In both cases the child’s British nationality is untouched, since neither country demands renunciation.

II. How the Préfecture Judges Your File — and How to Fight a Refusal

Eligibility gets you through the door; assimilation (assimilation à la communauté française) decides whether you stay in the room. Every file ends on the desk of an official who asks one question: has this Briton genuinely joined the French community? The answer is built from language, civic knowledge, work, conduct and family anchoring — tested at an interview you cannot retake lightly — and the same answer, if negative, comes back as one of three decisions: inadmissibility (irrecevabilité), postponement (ajournement) or rejection (rejet). Each has its own appeal path, and the courts overturn the administration every year when it overreaches. This section takes the test first, then the remedies.

A. The Assimilation Test: French at B2, the Civic Exam, the Interview, Work and Good Character

The statute sets the standard in deliberately broad words. Article 21-24 of the Civil Code states: “Nul ne peut être naturalisé s’il ne justifie de son assimilation à la communauté française, notamment par une connaissance suffisante, selon sa condition, de la langue, de l’histoire, de la culture et de la société françaises, dont le niveau et les modalités d’évaluation sont fixés par décret en Conseil d’Etat, et des droits et devoirs conférés par la nationalité française ainsi que par l’adhésion aux principes et aux valeurs essentiels de la République.” Language, history, culture, rights and duties, Republican values: the five pillars recur in every refusal letter, so take each literally.

Language first, because it sinks more British files than any other ground. The current requirement, confirmed by the service-public.fr guide, is demanding: you must show spoken and written French at least equal to level B2 of the Common European Framework of Reference for Languages (CECRL) — independent user, able to argue, write and follow abstract discussion, proved by a French diploma or a certified language test attestation. B2 in writing surprises Britons who have chatted happily at the market for a decade: conversational fluency is roughly B1, and the administration now fails candidates who cannot write correct French. Judges enforce the level as it stood at the date of the decision: in a 2021 ruling the Administrative Court of Appeal of Nantes recalled that under the version then applicable, “Tout demandeur doit justifier d’une connaissance de la langue française caractérisée par la compréhension des points essentiels du langage nécessaire à la gestion de la vie quotidienne et aux situations de la vie courante ainsi que par la capacité à émettre un discours simple et cohérent sur des sujets familiers dans ses domaines d’intérêt” — and upheld the inadmissibility of a Moroccan applicant whose driving licence points and years in France could not make up for an insufficient level (CAA Nantes, 5 November 2021, No 20NT01135). The lesson for a Briton is blunt: book the certified test early, prepare the written part seriously, and do not file until the certificate is safely above the threshold. Age over 60, chronic illness or a francophone diploma can adjust how the level is checked at the interview, but they do not waive it.

Next comes civic assimilation, verified twice: by a formal civic exam (examen civique) and by the individual interview (entretien individuel) at the prefecture or the naturalisation platform. Expect questions on the history of the Republic, the symbols and principles of the Constitution of 1958, laïcité (secularism), equality between women and men, the organisation of powers, and the rights and duties of a citizen. Article 21-25 of the Civil Code frames the machinery: “Les conditions dans lesquelles s’effectuera le contrôle de l’assimilation et de l’état de santé de l’étranger en instance de naturalisation seront fixées par décret.” The interview is the decisive moment: an official checks your knowledge, probes your adherence to Republican values, and writes the report (compte rendu) on which the decision largely rests. Courts treat those reports as faithful records unless you prove otherwise — in the Nantes case above, the judges noted there was no proof the prefecture interview reports had misrecorded the applicant’s words. Prepare like an examination: know the dates, the institutions, the meaning of laïcité, and be ready to explain in French why you want to become French. Vague answers about sunshine and property prices are remembered, and not fondly.

Work and resources weigh heavily. Official guidance calls professional integration (insertion professionnelle) an essential condition: stable, sufficient income covering your household’s needs out of your tax household (foyer fiscal). A British retiree with a solid UK pension paid into a French account satisfies this comfortably; a younger Briton with patchy freelance income, long gaps, or undisclosed work does not. File three years of French tax notices, employment contracts or pension statements, and proof of health cover. Debts to the Treasury or undeclared rental income from a gîte are the kind of detail that turns a borderline file into a postponement.

Conduct closes the test. Article 21-23 requires good life and morals (bonnes vie et mœurs): “Nul ne peut être naturalisé s’il n’est pas de bonnes vie et moeurs ou s’il a fait l’objet de l’une des condamnations visées à l’article 21-27 du présent code.” And Article 21-27 sets automatic bars: “Nul ne peut acquérir la nationalité française ou être réintégré dans cette nationalité s’il a été l’objet soit d’une condamnation pour crimes ou délits constituant une atteinte aux intérêts fondamentaux de la Nation ou un acte de terrorisme, soit, quelle que soit l’infraction considérée, s’il a été condamné à une peine égale ou supérieure à six mois d’emprisonnement, non assortie d’une mesure de sursis.” A prison sentence of six months or more without suspension, an unlifted deportation order, or a terrorism conviction blocks the route by law. Below that threshold the administration still weighs your record: recent drink-driving convictions, unpaid fines, or findings of fraud darken the picture. Order a copy of your criminal record (bulletin du casier judiciaire) before filing so there are no surprises.

The values cases show how the assimilation test bites in real life. On 26 November 2024 the Council of State (Conseil d’État, France’s supreme administrative court) upheld an opposition decree against a woman who, in the judges’ words, “a organisé sa vie dans le cadre exclusif de sa communauté, en dehors de toute volonté de mixité sociale en choisissant d’adopter un mode de vie incompatible avec les valeurs essentielles de la société française et notamment avec le principe d’égalité des sexes” (CE, 26 November 2024, No 492999). Similar rulings confirmed oppositions where prefecture interviews showed applicants did not subscribe to the essential values of French society (CE, 5 April 2019, No 418734; CE, 20 March 2023, No 461575). These were marriage-route cases, but prefectures apply the identical values grid to decree applications. For British readers the message is reassuring rather than alarming: an ordinary integrated life — working or retired in France, speaking French, children in French schools, respect for equality and secularism in public life — passes. What fails is the enclosed life: no French, no local ties, and statements at interview rejecting equality between women and men or the laws of the Republic.

B. Refusal, Postponement and Appeals: the Compulsory First Appeal, the Nantes Court and the Council of State

An unfavourable decision comes in three forms, and confusing them is the most common procedural mistake. Inadmissibility (irrecevabilité) means a legal condition was missing at filing — typically the five years, the residence permit or the language certificate — so the file is set aside without examination of its merits. Postponement (ajournement, usually two years) means the file was examined but the administration wants to see change: better French, steadier work, a cleaner record, deeper roots. Rejection (rejet) closes the application on its merits. The letter must state the legal and factual grounds and the available remedies (voies et délais de recours): read it with a lawyer before the clock starts, because every appeal has a two-month fuse.

The first appeal is compulsory and goes to the minister, not to a judge. Article 45 of the Decree of 30 December 1993 (Decree No 93-1362, the procedural code for nationality decisions) makes the hierarchical appeal (recours hiérarchique) to the minister in charge of naturalisations a mandatory gateway: as the Administrative Court of Appeal of Nantes recalled, “Ce recours, pour lequel le demandeur peut se faire assister ou être représenté par toute personne de son choix, doit exposer les raisons pour lesquelles le réexamen de la demande est sollicité. Il constitue un préalable obligatoire à l’exercice d’un recours contentieux, à peine d’irrecevabilité de ce dernier.” Skip it and go straight to court, and the judge will declare your case inadmissible without reading it. The same ruling recalls the second half of the mechanism: “Le silence gardé par le ministre chargé des naturalisations sur ce recours pendant plus de quatre mois vaut décision de rejet du recours.” Four months of ministerial silence equals rejection, and only then does the court door open. In practice: if you filed on paper, send the minister a reasoned appeal within two months of notification, by tracked post, answering each ground precisely with fresh evidence. If you filed online, the unfavourable decision is served in your personal space (espace personnel, “Mes notifications”) and the appeal must be lodged through the online form in that same space within two months — the official guide warns that an appeal sent by any other channel may be declared inadmissible unless a proven technical impossibility forced your hand.

The court stage belongs to Nantes. Appeals against naturalisation refusals and postponements go to the Administrative Court (tribunal administratif) of Nantes, which has national jurisdiction for this litigation, with further appeal to the Administrative Court of Appeal of Nantes. The judges review the file as it stood on the day of the decision: was the reasoning factually correct, was the law correctly applied, and — for postponements — was the assessment manifestly wrong (erreur manifeste d’appréciation)? The administration enjoys a wide margin on assimilation, and judges regularly confirm postponements where the record justifies prudence: on 23 May 2025 the Nantes court of appeal upheld a two-year postponement confirmed by the minister where recent criminal convictions, by their gravity and their closeness to the decision date, justified waiting despite the applicant’s family ties and professional record (CAA Nantes, 23 May 2025, No 24NT00188). Do not read such rulings as discouragement; read them as instructions. A postponement grounded in facts you can change — language, earnings, record — is an invitation to reapply stronger, and the judges say so implicitly every time they confirm one.

And the administration loses when it cannot prove its own case — which is where British applicants should take heart. On 29 May 2026 the Council of State annulled an opposition decree outright: “Il ne ressort pas des éléments versés au dossier par le ministre de l’intérieur que M. A… adopte un comportement ou soutient des thèses manifestant un rejet des principes essentiels de la République ou se tient délibérément à l’écart de la communauté nationale.” No evidence of rejection of Republican principles, no deliberate withdrawal from the national community: the decree fell (CE, 29 May 2026, No 502717). The ruling restates the division of labour that governs every challenge: the minister must put concrete material in the file, and bare assertions of “failed assimilation” do not survive review. Note also what the judges refused: the applicant had asked the court to order the state to grant him nationality, and the Council replied that annulling the decree implies no enforcement measure of its own — the file goes back for re-examination, and the claim for costs (3,000 euros under Article L. 761-1 of the Code of Administrative Justice) succeeded instead. Challenge to win the re-examination, not to collect the decree from the judge’s hands.

A practical appeal checklist for a Briton holding a refusal letter: first, diary the two-month deadline from notification and identify the correct channel (online form or ministerial post). Second, obtain the full file reasoning — the interview report, the language assessment, the investigation findings — and test each assertion against documents: tenancy agreements, tax notices, pay slips, school certificates, the language attestation, evidence of community life. Third, fix what can be fixed before the minister decides: retake the language test and score above B2, regularise any tax or fine arrears, gather proof of associations, local mandates or voluntary work. Fourth, frame the ministerial appeal as a re-examination request with numbered exhibits, not as a complaint: answer every ground, concede nothing you can contest, and show the trajectory since the decision. Fifth, if the minister rejects expressly or by four months’ silence, file with the Administrative Court of Nantes through a lawyer versed in nationality litigation, asking for annulment and re-examination. Throughout, keep your residence permit valid: an expired permit during the procedure hands the administration a fresh ground it did not have to invent.

Conclusion

For a Briton settled in France, naturalisation by decree is the definitive answer to Brexit’s paperwork: one application, one decree, and the full rights of a French citizen — European Union citizenship included — without surrendering anything in London. The conditions are exacting but legible: five years of genuinely French-centred life (two in the favoured cases, none in the exempt ones), residence in France at the signature of the decree, spoken and written French at B2, a convincing civic interview, stable resources, and a clean record. Dual nationality is accepted on both sides of the Channel, the marriage route offers a declaration-based alternative for spouses of French citizens, and children born or raised in France have their own paths that dovetail with yours. When the administration says no, waits you out with a postponement, or opposes a marriage declaration, the procedure gives you a real second act: a reasoned appeal to the minister within two months, then the judges of Nantes and, if needed, the Council of State — which annuls decisions the file cannot support, as its 29 May 2026 ruling demonstrates. Prepare the file like the examination it is, appeal a refusal like the litigation it can become, and take advice early: the difference between a postponement and a decree is rarely the life you have lived, and almost always the file you present.

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