You arrived before Brexit, or after it on a visa, and France is now home: the house, the carte de séjour (residence permit), the grandchildren at the local école (school). The next question many British residents ask is whether they can become French — to vote, to travel on a French passport, to stop renewing permits. The answer is yes, principally through naturalisation par décret (naturalisation by government decree): a discretionary grant, not a right, decided after a file, an investigation and an interview. This guide explains, in plain English with every French term defined, the three locks on the door — five years of habitual residence, assimilation crowned by B2 French, and a clean record — and then the procedure, the two kinds of refusal, and how each is challenged, up to the tribunal administratif de Nantes (the Nantes administrative court, which alone hears these appeals) and the Conseil d’État (France’s highest administrative court). Two recent rulings, quoted word for word, show where judges draw the line.

The short version first. You need habitual residence (résidence habituelle) in France for the five years before you apply, and you must still live here when the decree is signed; two years can suffice with a French higher-education diploma or exceptional integration. You must prove assimilation (assimilation à la communauté française), now tested by an examen civique (civic exam) plus a préfecture (local state authority) interview, B2 French spoken and written, stable professional integration, and signing the charte des droits et devoirs du citoyen français (charter of the French citizen’s rights and duties). Serious criminal convictions, an unlifted expulsion order or irregular stay bar you outright. A refusal comes in two flavours — irrecevable (inadmissible: a legal condition is missing, reapply when fixed) or inopportune (rejected or ajournée, postponed, typically two years) — and each has its own appeal ladder ending, for online filers, in a mandatory hierarchical appeal (recours hiérarchique) then Nantes. Britain, for its part, fully allows dual nationality, as the British government confirms in its dual-citizenship guidance: the United Kingdom allows dual nationality, so applying for French citizenship means keeping the British one too. France raises no objection either, so you keep both passports.

I. Can I become French after Brexit, and what must I show?

A. How long must I have lived in France, and who is barred outright?

The gateway provision is Article 21-15 of the Code civil (the civil code): apart from a special case that does not concern Britons, “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.” Nationality by public decision comes from a decree granted at the foreigner’s request. Note the word granted: unlike a birthright declaration, naturalisation is a favour (une faveur), and the administration enjoys, in the courts’ settled phrase, a wide discretion — a point the case law below confirms, within limits.

The residence lock has two bolts. Article 21-17 requires, subject to exceptions, that “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 before filing. Article 21-16 adds: “Nul ne peut être naturalisé s’il n’a en France sa résidence au moment de la signature du décret de naturalisation” — you must still reside in France when the decree is signed. For Britons this holds two practical consequences. First, years lived in France as an EU citizen before 2021 count: the statute asks for habitual residence, not for years under a particular permit, so a Londoner settled in Lyon since 2016 easily clears the stage. Second, keep the centre of your life here until the Journal officiel (the official gazette where decrees are published) carries your name — moving back to Kent mid-file invites refusal, and the official guidance warns expressly that where a spouse or children remain abroad, nationality “peut vous être refusée” (may be refused). The préfet (the state’s county-level representative) checks where your family actually lives.

Three groups move faster. Article 21-18 cuts the stage to two years for anyone who completed two years of higher education for a French university diploma, who renders or can render important services to France through ability and talent, or who shows an exceptional integration record in civic, scientific, economic, cultural or sporting life. Article 21-19 waives the stage entirely for narrow cases — effective service in a French army unit, exceptional services to France (then only after the Conseil d’État gives its opinion), or recognised refugee status. A British graduate of a Bordeaux université (university) with a master’s after two years, or a researcher whose work France celebrates, should claim the two-year lane expressly rather than waiting out five.

The bars are absolute and checked first. Article 21-27 provides that no one may acquire French nationality after convictions for crimes or offences against the Nation’s fundamental interests or terrorism, or — whatever the offence — after a prison sentence of six months or more without suspension (sans sursis, unsuspended); the same exclusion hits anyone under a live expulsion order (arrêté d’expulsion), an unexecuted ban from French territory (interdiction du territoire français), or in irregular stay (séjour irrégulier). British applicants with an old English conviction must therefore count months, not just years: a nine-month custodial sentence in England, however dated and however spent under British rehabilitation law unless French rehabilitation (réhabilitation) has operated, blocks the decree. Lesser records do not trigger the automatic bar but feed the discretionary assessment — declare everything, because the file check (enquête, the background investigation) will find it, and concealment itself destroys trust.

B. How do I prove assimilation: B2 French, the civic exam, the interview and the job?

Assimilation is the heart of the file, and since the recent reforms it is examined harder than most Britons expect. Article 21-24 states, word for word: “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.” No one may be naturalised without proving assimilation to the French community — language, history, culture and society at a level set by decree, knowledge of the rights and duties of nationality, and adhesion to the Republic’s essential principles and values. The same article pins the language bar in statutory language: “L’intéressé justifie d’un niveau de langue lui permettant au moins de comprendre le contenu essentiel de sujets concrets ou abstraits dans un texte complexe, de communiquer avec spontanéité, de s’exprimer de façon claire et détaillée sur une grande variété de sujets.” That is B2 on the European scale (le CECRL, the Common European Framework): understand complex texts, converse spontaneously, argue clearly and in detail. The service-public.fr guidance, verified in January 2026, confirms the current rule without ambiguity: for nationality by decree you must show French “au moins égale au niveau B2”, oral and written (à l’oral et à l’écrit). The old conversational B1 is gone; a British retiree whose French stops at market shopping must study to examination standard.

Prove the level with the right paper, recent enough. The guidance accepts a French state diploma (diplôme français) or a pass certificate from an approved language test (attestation de réussite à un test linguistique), and the case law below shows certificates older than two years are treated as stale — sit the test inside the two-year window before filing. Exemptions exist and matter: native French speakers, those schooled five-plus years in French, former French servicemen and the over-65s with long residence follow eased tracks the guidance details — check the exemption list before paying for a test you may not need.

Language is necessary but not sufficient. Assimilation is now verified twice: by passing the examen civique (the civic exam on the Republic’s principles, values and symbols) and by the entretien en préfecture (the prefecture interview), whose purpose the guidance describes as checking assimilation, adhesion to the essential principles and values of the Republic, and knowledge of civic essentials — followed by signing the charter. Article 21-25 frames this control by decree. Then comes the factor that sinks more British files than any other: l’insertion professionnelle (professional integration). The guidance calls it “une condition essentielle”: you must show stable, sufficient income (des revenus stables et suffisants) supporting yourself and your family. A comfortably off early retiree with pensions and property usually passes; a newcomer between contracts, living on savings with no French tax history, should wait until payslips (fiches de paie) or audited accounts establish durability. Finally, keep the file alive: any change of address, job or family situation must be declared to the naturalisation platform (la plateforme de naturalisation) during examination, and you will need originals of every civil-status document (actes d’état civil, full birth and marriage certificates with translations) at the interview.

II. How does the file move, and how do I challenge a refusal?

A. From filing to the decree: the platforms, the interview and the two kinds of no

File online through your personal account (espace personnel) to the naturalisation platform serving your département (administrative county) — Paris and Île-de-France applicants use the platform covering their home county, listed on the official platform map — or by post where the online route is closed to you. You receive a filing receipt (un récépissé), then, if the file is receivable, a summons to the assimilation interview. Behind the scenes the prefecture investigates, the file rises to the nationality sub-directorate (la sous-direction de l’accès à la nationalité française, SDANF) under the interior ministry, and the decision comes as a decree published in the Journal officiel — or as one of three unfavourable outcomes you must learn to distinguish, because each dictates a different remedy.

The guidance draws the map. Your request is irrecevable (inadmissible) where a legal condition is simply unmet — short residence, missing B2 certificate, unlifted criminal bar. Cure the defect and file again: once the ground for inadmissibility has disappeared, a fresh application is open to you. It is inopportune (inopportune, meaning grantable in law but refused in discretion) where nationality is “pas, ou pas encore, envisageable” — not, or not yet, conceivable. Then the administration either rejects outright (rejetée, a rejet) or postpones (ajournée, an ajournement): A postponement sets a waiting period — for example to strengthen professional integration — after which a new application may be filed. The classic two-year ajournement tells a young worker to return with two years of payslips, a B2 certificate, or a settled family situation. Respect the cooling rules the guidance states: after a rejection for inopportunity, a fresh file within five years of notification may be closed without examination (classée sans suite) absent new circumstances; after an ajournement, refiling before the imposed delay expires meets the same fate. Every unfavourable decision must be reasoned (motivée) and must state the avenues and deadlines of appeal (les voies et délais de recours) — check the letter for both, because a missing remedy notice is itself a handle for challenge.

Even success carries strings. The decree may be withdrawn within two years of publication in the Journal officiel, on the Conseil d’État’s concurring opinion, if the conditions were not met — and within two years of discovery in case of fraud (fraude). Declare the English conviction, the child living in Manchester, the months spent outside France: what the investigation would have found, the withdrawal procedure will find later at far greater cost. Once French, a young new citizen aged sixteen to twenty-five must register for national service census (se faire recenser) within the month — a small formality, but one the guidance flags because newcomers miss it.

B. How to fight each refusal: the hierarchical appeal, Nantes, and what judges actually control

The appeal ladder depends on how you filed. The guidance explains that a prior administrative appeal to the minister is not in principle compulsory before going to court — direct court action is possible — but for online filers the next paragraph makes the hierarchical appeal (recours hiérarchique) effectively the first step, with teeth: two months from online notification (notification) to appeal to the minister through the form in your personal space, failing which, save proven technical impossibility, the appeal “pourra être déclaré irrecevable”. Then the clockwork: if the minister says no, or stays silent four months (en l’absence de réponse dans un délai de 4 mois), you have two months for the court appeal (recours contentieux) “devant le tribunal administratif de Nantes”. Keep the acknowledgement of receipt (l’accusé de réception, AR) of the hierarchical appeal: in silence cases the two months run from proof of that receipt, and the court named is always Nantes, wherever in France — Paris included — you live.

Two rulings show how judges use that jurisdiction, and both are worth reading whole. First, the Conseil d’État on reasons and values: on 11 July 2023, Second Chamber, no. 466865 (ECLI:FR:CECHS:2023:466865.20230711), ruling on a ministerial refusal grounded in defective assimilation, the Court first upheld the form — “le décret attaqué énonce les considérations de droit et de fait sur lesquelles il se fonde. Il est ainsi suffisamment motivé.” The decree stated the legal and factual considerations behind it and was therefore sufficiently reasoned. It then approved the substance: faced with precise, clear and circumstantial material — contacts with terrorist-linked individuals minimised at interview, and a lifestyle “caractérisé par une soumission des femmes qui ne correspond pas aux valeurs de la société française, notamment l’égalité entre les sexes” — the Prime Minister “n’a pas fait une inexacte application” of the assimilation test. The lesson for British applicants is double-edged but clear: the administration must spell out its reasons, which gives you something to answer, while adhesion to republican values — equality between the sexes first among them — is controlled as strictly as language. Prepare the interview as an examination in values, not a chat.

Second, the Nantes appeal court on procedure and proportionality: on 28 January 2025, 6th Chamber, no. 24NT00727 (CAA Nantes, 24NT00727), annulling a two-year ajournement imposed by the Hautes-Pyrénées prefect on language-and-culture grounds. The court recalled the governing frame, word for word: “L’autorité administrative dispose, en matière de naturalisation ou de réintégration dans la nationalité française, d’un large pouvoir d’appréciation.” A wide discretion — but not an unlimited one, for the same paragraph continues, word for word: “Pour rejeter une demande de naturalisation ou de réintégration dans la nationalité française, l’autorité administrative ne peut se fonder ni sur l’existence d’une maladie ou d’un handicap.” Illness or disability may never ground the refusal. Applying that to medical certificates showing autism with severe intellectual disability and no acquired language at all, the court held, word for word, that the prefect “ne pouvait légalement opposer à la requérante, par sa décision du 21 août 2023, sa connaissance insuffisante des éléments fondamentaux relatifs à l’histoire et à la culture française à l’issue d’un entretien oral, cette insuffisance résultant en réalité directement du handicap de l’intéressée.” The ajournement and the minister’s rejection of the hierarchical appeal were both annulled, with an order (injonction) to re-examine within two months and €1,500 costs against the State. The same judgment is a procedure manual: it censured the Nantes tribunal for rejecting the case over a missing copy of the hierarchical appeal where the minister’s own letter proved one had been filed, and treated the minister’s platform-direction letter as the appeal decision itself. For your file, the morals are concrete — attach proof of every appeal step, plead disability exemptions with the prescribed joint-ministry medical certificate (certificat médical), and never accept that a requirement you cannot physically meet was fairly applied to you.

Fight in this order. First, classify the decision the day it arrives: irrecevable means fix-and-refile; rejet or ajournement means hierarchical appeal within two months, then Nantes within two months of the express or four-month-implied answer. Second, answer the stated reason only — language, insertion, family centre, values — with dated paper: fresh B2 certificate, twelve months of payslips and tax notices (avis d’imposition), school certificates for the children, the French spouse’s nationality proof. Third, plead the two rulings where they fit: defective or boilerplate reasoning against the 2023 Conseil d’État standard, disability or health-based reasoning against the 2025 Nantes standard. Fourth, watch your own conduct pending appeal: hold residence, keep declaring changes to the platform, and do not let the passport expiry push you into irregular stay, because Article 21-27 would then bar you outright. The administration’s discretion is wide, but as Nantes shows, it is a controlled width — and a reasoned, documented appeal crosses it.

Conclusion

Naturalisation rewards the settled, not the hurried. Five years of habitual residence with residence intact at decree day, B2 French proved by a recent certificate, a passed civic exam and a convincing values interview, stable professional integration, and a record without the statutory bars — that is the whole door, and the Withdrawal Agreement generation of Britons, resident since before 2021, already holds the five-year key. Meet an irrecevable by curing it, meet a rejet or ajournement with the two-month hierarchical appeal and then Nantes, and hold the administration to reasoned decisions and lawful grounds. Done in that order, the British applicant stops being a permanent resident by permission and becomes a citizen by decree — keeping the British passport alongside the French one, since British guidance allows dual nationality. Start the language test now even if your five years are not yet complete, because a B2 certificate younger than two years must be in the envelope on filing day, and a stale certificate is the commonest avoidable irrecevable.

Need a quick opinion on your case

A 20-minute telephone consultation with a lawyer of the firm, within 48 hours, to review your residence history, your language evidence and your deadline to challenge a refusal or ajournement. Call +33 6 46 60 58 22 or write via our contact page. We advise British applicants across Paris and Île-de-France.