Since the end of the Brexit transition period, British citizens living in France have discovered that a carte de séjour (residence permit), even a Withdrawal Agreement card, is only ever a permission to stay. It can be lost, it must be renewed, and it leaves you a foreigner in the country where you pay your taxes, run your business and raise your children. For a growing number of Britons, the next step is full membership: becoming French while keeping British citizenship, so that no future change in immigration rules can ever unsettle the family again. The route is called naturalisation par décret, naturalisation by decree, and it is governed by Articles 21-15 to 21-27 of the French Civil Code. It is a favour granted by the French State, never a right, which means the administration can say no even when every box appears ticked. This article explains who can apply, what the prefecture actually checks, how the file moves from the online portal to the decree signed in Paris, and, above all, what to do when the answer is a refusal or an ajournement (adjournment): the two-month hierarchical appeal to the minister and the court action before the administrative court of Nantes. If you are still at the visa stage, our guide to which long-stay visa leads to a carte de séjour and how to challenge a refusal covers the first steps of the journey.

I. Can a British citizen become French after Brexit, and what does France check?

A. Five years of French life, the centre of your interests in France and a clean criminal record

The starting point is simple to state and demanding to prove. Under Article 21-15 of the Civil Code, and I quote, “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” — acquisition of French nationality by decision of the public authority results from naturalisation granted by decree at the foreigner’s request. Three words matter here: à la demande, on request, and par décret, by decree. Nobody is naturalised automatically, and nobody has a right to be naturalised. The minister decides, and the courts only review the legality of that decision, which is why refusals are so often challenged on procedural grounds, as explained in Part II.

The first substantive condition is residence. Article 21-16 of the Civil Code provides, and I quote, “Nul ne peut être naturalisé s’il n’a en France sa résidence au moment de la signature du décret de naturalisation” — no one may be naturalised unless he or she is resident in France when the naturalisation decree is signed. Residence is therefore checked twice: when you apply and again on the day the decree is signed, so moving back to the United Kingdom while the file is being examined can be fatal to it. More precisely, Article 21-17 of the Civil Code requires, and I quote, “une résidence habituelle en France pendant les cinq années qui précèdent le dépôt de la demande” — habitual residence in France during the five years before the application is lodged. This is the famous five-year stage, the qualifying period. For British applicants, the clock normally starts on the date real settlement in France began, evidenced by leases, tax notices, school certificates and employment records, not by the date a Withdrawal Agreement card was issued. Periods spent abroad break continuity if they show that the centre of your life moved away: long secondments back to London, a family home kept and lived in across the Channel, or children schooled in England while the applicant lives nominally in France are the classic reasons files fail at this stage.

The prefecture applies a doctrine with an old-fashioned name, the centre des intérêts matériels et moraux, the centre of your material and moral interests. The official guidance on the service-public.fr portal states it plainly: you must have in France the centre of your material interests, including professional ones, and your family ties, and it warns that if you reside in France but your spouse or children reside abroad, you may be refused French nationality. In practice, the examining officer, known as the agent instructeur, builds a picture from your tax returns, your employment contracts or business accounts, your children’s school enrolments and your spouse’s own residence status. A British executive who kept his family in Surrey, commutes weekly on Eurostar and files as a French resident only on paper will struggle to convince anyone that France is the centre of his life. Conversely, a retired couple in the Dordogne whose children visit for Christmas, whose taxes are paid in France under the France-United Kingdom double tax treaty and whose medical care runs through the French health system presents exactly the settled profile the procedure was designed for.

The five-year period can be shortened in defined cases. Article 21-18 of the Civil Code reduces the stage to two years, and I quote the three cases, “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 foreigner who successfully completed two years of higher education for a French diploma, one who has rendered or can render important services to France through ability and talent, or one with an exceptional integration record in civic, scientific, economic, cultural or sporting life. British graduates of French universities and Britons with distinguished professional or voluntary records in France should examine this provision closely, because two years instead of five changes the entire timetable of a family’s plans. No qualifying period at all applies in the situations listed in Article 21-19 of the Civil Code, notably service in the French army and recognised refugee status, and in Article 21-20 of the Civil Code for nationals of French-speaking states whose mother tongue is French or who were schooled five years in French — provisions of limited use for most British applicants but worth knowing where a spouse holds a second, francophone nationality.

Two further filters apply before the merits are even weighed. First, regularity of stay: you must hold a valid residence permit when you apply, and any expulsion order or ban from French territory still in force bars acquisition outright. Second, good character. Article 21-27 of the Civil Code excludes anyone convicted of crimes or offences against the fundamental interests of the Nation or of terrorism, anyone sentenced to six months’ imprisonment or more without suspension for any offence, anyone under an unlifted expulsion order or an unexecuted territory ban, and anyone whose stay is irregular. The text adds an important qualification: rehabilitation, whether automatic or judicial, and removal of the conviction from bulletin no. 2 of the casier judiciaire, the French criminal record, restore eligibility. British applicants who have lived in France for fewer than ten years must also produce the original of their foreign criminal record, which in practice means a United Kingdom police certificate alongside any other country of residence, and a drink-driving conviction or a suspended sentence needs to be assessed honestly before filing, because the prefecture will see bulletin no. 2 and draw its own conclusions. Professional integration completes the picture: the administration expects stable and sufficient lawful income supporting the whole household, so a file showing reliance on benefits, undeclared work or chronic overdrafts invites an adjournment on economic grounds even where the legal conditions are technically met.

B. Assimilation: the language test, the civic exam and the prefecture interview

Even a applicant with ten years of flawless residence can be refused for lack of assimilation à la communauté française, assimilation into the French community, and this is where British files most often stumble. Article 21-24 of the Civil Code, in its version in force since 1 January 2026, provides, and I quote, “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, notably through sufficient knowledge, relative to his or her situation, of the French language, history, culture and society, assessed under conditions set by decree in the Conseil d’Etat, and through knowledge of the rights and duties of French nationality and adherence to the essential principles and values of the Republic. The same article then raises the bar in strikingly concrete terms, and I quote again: “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” — the applicant must show a command of French sufficient to understand the essential content of concrete or abstract subjects in a complex text, to communicate spontaneously, and to express himself or herself clearly and in detail on a wide variety of subjects. Readers familiar with the Common European Framework will recognise level B2, independent user moving toward fluent interaction, a real step above the old conversational standard. For a British retiree who has lived for years in an English-speaking enclave, shopping in English and socialising in English, this requirement is the single most dangerous part of the file, and preparation should begin a year or more before applying: certified diplomas and attestations from approved bodies such as the DELF B2, structured conversation practice on abstract subjects like laïcité or the organisation of French institutions, and regular reading of French press, because the examiner will deliberately move the conversation beyond daily life toward precisely those concrete and abstract subjects the statute names.

Assimilation is verified through three linked exercises. First, the examen civique, the civic examination, a test of knowledge about French history, culture, society and the rights and duties attached to nationality, for which the service-public.fr portal publishes the official syllabus and a certificate of success must be attached to the file. Second, the language diploma or attestation proving the required level, obtained from an approved examination centre before filing, since the prefecture will not wait for you to sit the test afterwards. Third, the entretien d’assimilation, the assimilation interview at the prefecture, where an officer assesses in person whether the paper file matches a real person anchored in French life. Candidates consistently underrate this interview. It is conducted entirely in French, it probes knowledge of republican values, of the organisation of the State and of everyday civic life, and its written report colours every later stage of the procedure, including the minister’s final decision. Practical preparation means knowing the names and roles of the President, the Prime Minister and your mayor, understanding what the 1789 Declaration, the tricolour and the Marseillaise represent, being able to explain why your children’s schooling, your associations and your working life sit in France, and answering frankly about any period of your life that looks unanchored. At the end of the assimilation check, the successful applicant signs the charte des droits et devoirs du citoyen français, the charter of the rights and duties of the French citizen, which, as Article 21-24 states, recalls the essential principles, values and symbols of the French Republic. The signature is not folklore; it is the statutory closing act of assimilation, and refusal to sign would itself demonstrate the absence of the adherence the law demands.

Two British-specific points deserve emphasis. The first is the spouse abroad trap. Where a British applicant lives in France but the husband, wife or children remain in the United Kingdom, the file reads as a centre of interests split across the Channel, and the official guidance expressly warns that nationality may be refused on that ground. Families in this position should either organise the move of the whole household before applying or assemble unusually strong evidence that France is genuinely the hub: French tax residence of the entire household, French schooling, French-language integration of each member and a credible explanation for any temporary separation. The second is professional life. Salaried employment with French payslips, a registered self-employed activity with regular declarations, or a solid pension income with French tax returns all reassure; by contrast, remote work paid from London into a British account with no French footprint, unexplained gaps in activity, or debts to the tax authorities or social security bodies raise questions that an otherwise sympathetic officer must record. None of these difficulties is automatically fatal, but each must be anticipated and documented, because the minister’s decision, and any later challenge to it, will be judged on the file as filed.

II. From the application to the decree, and what to do when the answer is no

A. The file, the fee, the investigation and the decree that makes you French

Naturalisation applications are now lodged online through the dedicated portal, although paper filing with the Cerfa form no. 12753 in duplicate remains possible and follows the same substantive rules. The file is heavy by design: proof of identity and nationality, civil status documents with translations and, where needed, the foreign decision behind them, proof of address, proof of resources and tax compliance, the language diploma, the civic examination certificate, documents on the couple and on minor children, and, for applicants present in France for fewer than ten years, the original foreign criminal record extract. A récépissé, an official receipt, is issued once the file is complete, and completeness matters: the examining service may set a deadline for producing missing documents or completing formalities, and a file left incomplete can be closed without examination, a classement sans suite, which is notified with its own appeal routes and must not be confused with a refusal on the merits. The procedure costs 255 euros, 127.50 euros in French Guiana, paid by timbre fiscal, the electronic tax stamp, and applicants should ignore the private websites that sell appointments or paid assistance around the prefectures: apart from the stamp, acquisition of French nationality is a free procedure, and paying an intermediary buys no priority whatsoever.

Once complete, the file enters a long investigation. The prefecture verifies every statement, consults the police and tax files, conducts the assimilation interview and sends a reasoned opinion to the central ministry department, the SDANF, the sub-directorate for access to French nationality, which prepares the minister’s decision. There is no statutory time limit for the decision itself, and eighteen to twenty-four months of waiting is ordinary; silence during this period is not a refusal and creates no appeal right, so patience, rather than premature litigation, is the correct posture while the file is genuinely under examination. If the outcome is favourable, naturalisation is granted by decree, published with your name, and takes effect on signature, provided you are resident in France that day as Article 21-16 requires. The decree has a collective effect on minor children that British parents should understand precisely. Article 22-1 of the Civil Code provides, and I quote, “L’enfant mineur dont l’un des deux parents acquiert la nationalité française, devient français de plein droit s’il a la même résidence habituelle que ce parent ou s’il réside alternativement avec ce parent dans le cas de séparation ou divorce” — a minor child one of whose parents acquires French nationality becomes French as of right if the child shares that parent’s habitual residence, or lives alternately with that parent after separation or divorce. The same article adds a condition that traps the unwary, and I quote, “Les dispositions du présent article ne sont applicables à l’enfant d’une personne qui acquiert la nationalité française par décision de l’autorité publique ou par déclaration de nationalité que si son nom est mentionné dans le décret ou dans la déclaration” — for acquisition by decision of the public authority, the child benefits only if named in the decree or declaration. Parents must therefore list every minor child in the application and check the published decree: a child forgotten at filing is not covered, and repairing the omission afterwards requires a separate procedure.

Becoming French does not mean ceasing to be British. The United Kingdom permits dual nationality without restriction: the official gov.uk dual citizenship guidance confirms that a British citizen may acquire another country’s citizenship and keep British citizenship, with no application for dual status itself required. France likewise tolerates dual nationality with the United Kingdom, so no renunciation is required on either side. One consequence deserves a clear warning, drawn from the same guidance: as a dual national, you cannot obtain British diplomatic help when you are in France, the country of your second citizenship. Practically, a newly naturalised Franco-British citizen travels on either passport, votes in both countries where eligible, and keeps full rights of residence and work in each, but should understand that in France he or she will henceforth be treated as French. Families should also consider the knock-on effects before applying: French nationality brings French civic obligations and, for estates and tax, confirms a French anchoring that complements, but does not replace, careful succession planning for any property kept in England.

B. Refusal or adjournment: the two-month appeal to the minister, then the court in Nantes

An unfavourable decision comes in two forms, and confusing them is the most common and costly mistake. The administration may declare your request irrecevable, inadmissible, where a legal condition is missing — no valid residence permit, insufficient years of residence, a disqualifying conviction — or inopportune, inopportune, where nationality is not, or not yet, conceivable on the merits: weak professional integration, doubtful assimilation, a centre of interests outside France. In the second case the decision may be a rejet, an outright rejection, or an ajournement, an adjournment imposing a waiting period, typically two years, to allow you to strengthen the weak point, for example by stabilising employment or improving French. The decision must be motivée, reasoned in law and fact, and the statement of reasons is the foundation of everything that follows: it tells you which ground to attack and which evidence to gather. Read it line by line with the file you submitted beside it, because many successful challenges begin with a reason that misstates the facts — years of residence miscounted, a diploma overlooked, tax documents misread — or applies the wrong legal test. Note also the five-year shadow cast by an inopportune refusal: a fresh application lodged within five years of notification may be closed without further examination unless new circumstances are shown, which makes the first challenge, rather than a hasty reapplication, the strategic priority.

The first remedy is the recours hiérarchique, the hierarchical appeal to the minister responsible for naturalisations, and the time limit is brutally short: two months from notification of the adverse decision. For online applicants, notification arrives in the personal area under notifications, and the appeal itself must be lodged through the form in that same personal area, faute de quoi it risks inadmissibility except for proven technical impossibility; for paper applicants, notification comes by registered letter or summons to the prefecture, and the appeal goes by post to the ministry. The appeal must confront each stated ground with dated evidence: corrected residence computation with supporting leases and tax notices, new language certification, employment contracts and payslips covering the criticised period, proof that the spouse and children have now joined the applicant in France, or rehabilitation documents neutralising an old conviction. Generic letters pleading attachment to France carry no weight; only documents that dissolve the stated reason do. If the minister answers negatively, or stays silent for four months — silence counts as an implicit rejection — a second two-month clock starts for the court action. Where the online route was used, the starting point is the notification of the negative decision, and the acknowledgment of the appeal should be kept to compute the four-month silence period precisely, because a court application lodged one day late is inadmissible whatever its merits.

The court with exclusive jurisdiction is the administrative court of Nantes. Article R312-18 of the Code of Administrative Justice provides, and I quote, “le tribunal administratif de Nantes est compétent pour connaître des recours dirigés contre les décisions du ministre chargé des naturalisations”, in appeals brought under Article 45 of the decree of 30 December 1993 — the Nantes administrative court hears challenges to the naturalisation minister’s decisions taken under Article 45 of the decree of 30 December 1993. A British resident of Nice, Lyon or Paris therefore litigates in Nantes, generally through a lawyer, and the judge reviews the refusal for legal error, factual error, manifest error of assessment and breach of procedural requirements including the duty to give reasons. Naturalisation remains a discretionary favour, so the court will not substitute its own view of who deserves to be French; it annuls decisions that rest on wrong facts, wrong law or reasoning so thin that it reveals no genuine examination. Annulment sends the file back to the minister for reconsideration and, in well-built cases, is accompanied by an injunction to re-examine within a set time, which is why the hierarchical appeal file must already be litigation-ready: every document you will need in Nantes should have been put before the minister first. Throughout, keep every notification, every acknowledgment and every envelope: in nationality litigation, limitation periods are computed to the day, and the applicant who kept nothing is the applicant who files late.

Conclusion

For a British citizen settled in France, naturalisation by decree is the definitive answer to Brexit insecurity: five years of genuine French life, the centre of material and family interests in France, a clean record, stable resources, proven command of French at the level Article 21-24 now demands, and success in the civic examination and the prefecture interview. The procedure rewards the well-documented and the patient, from the 255-euro tax stamp to the decree that can carry minor children with it where they are named. Its dangers are equally clear: a household split across the Channel, an unprepared interview, a forgotten child on the application, and above all the two-month appeal clocks that start running the day a refusal or adjournment is notified. Because naturalisation is a favour and not a right, the minister’s reasons must be met with evidence rather than sentiment, first in the hierarchical appeal and, if needed, before the administrative court of Nantes. Prepared in this spirit, a British file does not merely request French nationality; it demonstrates, document by document, that the applicant already lives as a French citizen in everything but law.