Since the end of free movement, many British citizens living in France have asked themselves the same question: should I become French? A French passport removes the residence-permit cycle, secures your right to stay whatever happens to your Withdrawal Agreement card, opens full voting rights, and simplifies travel in and out of the Schengen area. But French nationality is not handed out on request. It follows strict statutory routes, each with its own residence clock, language threshold and documentary traps. This article explains, for a British reader, the two routes that matter in practice after Brexit: naturalisation by decree and declaration of nationality through marriage to a French spouse. It then sets out how refusals and oppositions work, how a court recently annulled an opposition based on a vague claim of non-assimilation, and what becoming French changes for your British passport and daily life. Every French legal term is explained as it appears.<\/p>\n
Naturalisation by decree (naturalisation par d\u00e9cret) is the standard route for a British citizen with no French family link. The Civil Code states the principle in short terms: “Hors le cas pr\u00e9vu \u00e0 l’article 21-14-1 , l’acquisition de la nationalit\u00e9 fran\u00e7aise par d\u00e9cision de l’autorit\u00e9 publique r\u00e9sulte d’une naturalisation accord\u00e9e par d\u00e9cret \u00e0 la demande de l’\u00e9tranger.” (article 21-15 of the Civil Code<\/a>). Three points in that sentence deserve attention. First, nationality is granted by decree, which means the administration exercises a discretion: meeting the conditions makes you eligible, but the decision remains an individual measure that can be refused with reasons. Second, it is granted only on application (\u00e0 la demande de l’\u00e9tranger): nothing is automatic, and since the procedure moved online you must file through the NATALI teleservice rather than at a prefecture counter. Third, it is a decision of the public authority, which means it can be challenged before the administrative courts if it is unlawful.<\/p>\n The residence clock is the first substantive condition. The Code provides: “Sous r\u00e9serve des exceptions pr\u00e9vues aux articles 21-18 , 21-19 et 21-20 , la naturalisation ne peut \u00eatre accord\u00e9e qu’\u00e0 l’\u00e9tranger justifiant d’une r\u00e9sidence habituelle en France pendant les cinq ann\u00e9es qui pr\u00e9c\u00e8dent le d\u00e9p\u00f4t de la demande.” (article 21-17 of the Civil Code<\/a>). For a British citizen who arrived after 1 January 2021, the five years run from genuine settlement, not from occasional stays: the administration looks at where your home, work, tax residence and family life actually are. A companion rule adds: “Nul ne peut \u00eatre naturalis\u00e9 s’il n’a en France sa r\u00e9sidence au moment de la signature du d\u00e9cret de naturalisation.” (article 21-16 of the Civil Code<\/a>). Moving back to the United Kingdom while your file is being examined therefore puts the decree itself at risk, even if the five years were complete when you applied.<\/p>\n The five-year period (stage) can be shortened in defined cases. It is reduced to two years for a foreigner who has successfully completed two years of higher education leading to a diploma awarded by a French university or higher education establishment, for a person who has rendered or can render important services to France by ability and talent, and for a foreigner showing an exceptional path of integration assessed through civic, scientific, economic, cultural or sporting activity: “Le stage mentionn\u00e9 \u00e0 l’article 21-17 est r\u00e9duit \u00e0 deux ans : 1\u00b0 Pour l’\u00e9tranger qui a accompli avec succ\u00e8s deux ann\u00e9es d’\u00e9tudes sup\u00e9rieures en vue d’acqu\u00e9rir un dipl\u00f4me d\u00e9livr\u00e9 par une universit\u00e9 ou un \u00e9tablissement d’enseignement sup\u00e9rieur fran\u00e7ais ; 2\u00b0 Pour celui qui a rendu ou qui peut rendre par ses capacit\u00e9s et ses talents des services importants \u00e0 la France ; 3\u00b0 Pour l’\u00e9tranger qui pr\u00e9sente un parcours exceptionnel d’int\u00e9gration, appr\u00e9ci\u00e9 au regard des activit\u00e9s men\u00e9es ou des actions accomplies dans les domaines civique, scientifique, \u00e9conomique, culturel ou sportif.” (article 21-18 of the Civil Code<\/a>). No residence period at all is required in narrower situations, including military service in a French army unit, exceptional services to France or a naturalisation presenting an exceptional interest for France, and recognised refugee status: “Peut \u00eatre naturalis\u00e9 sans condition de stage” (article 21-19 of the Civil Code<\/a>). Most British applicants will not fall into these exceptions and should plan for the full five years.<\/p>\n The second substantive condition is assimilation (assimilation \u00e0 la communaut\u00e9 fran\u00e7aise): language, knowledge of French history, culture and society, and acceptance of the rights, duties and values of the Republic. The current text of the Code sets a demanding language standard: “Nul ne peut \u00eatre naturalis\u00e9 s’il ne justifie de son assimilation \u00e0 la communaut\u00e9 fran\u00e7aise, notamment par une connaissance suffisante, selon sa condition, de la langue, de l’histoire, de la culture et de la soci\u00e9t\u00e9 fran\u00e7aises, dont le niveau et les modalit\u00e9s d’\u00e9valuation sont fix\u00e9s par d\u00e9cret en Conseil d’Etat, et des droits et devoirs conf\u00e9r\u00e9s par la nationalit\u00e9 fran\u00e7aise ainsi que par l’adh\u00e9sion aux principes et aux valeurs essentiels de la R\u00e9publique.” And: “L’int\u00e9ress\u00e9 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 spontan\u00e9it\u00e9, de s’exprimer de fa\u00e7on claire et d\u00e9taill\u00e9e sur une grande vari\u00e9t\u00e9 de sujets.” (article 21-24 of the Civil Code<\/a>). In plain terms, conversational holiday French is not enough: you must follow complex texts, react spontaneously and argue a point clearly. After the assimilation check, the applicant signs the charter of rights and duties of the French citizen (charte des droits et devoirs du citoyen fran\u00e7ais), which recalls the principles, values and symbols of the French Republic.<\/p>\n Language is where solid files most often fail. A ruling of the Nantes administrative court of appeal illustrates the method. The minister had declared a naturalisation application inadmissible because the applicant’s spoken French fell below the required level, and the court upheld that assessment: “Pour d\u00e9clarer irrecevable la demande de naturalisation pr\u00e9sent\u00e9e par Mme C… \u00e9pouse B…, le ministre charg\u00e9 des naturalisations a, sur le fondement de l’article 21-24 du code civil, estim\u00e9 que son niveau de connaissance de la langue fran\u00e7aise \u00e9tait insuffisant d\u00e8s lors qu’il \u00e9tait inf\u00e9rieur au niveau B1 oral requis par les dispositions de l’article 37 du d\u00e9cret du 30 d\u00e9cembre 1993.” The court noted that the prefecture interview showed she had been unable to answer on familiar subjects linked to her personal or professional interests, to give her opinion, or to recount the plot of a film, a book or an unexpected event (CAA Nantes, 5 November 2021, no. 20NT01135, full text on L\u00e9gifrance<\/a>). The lesson for British applicants is practical: the prefecture interview is a genuine examination, and a language certificate below the required level combined with a weak interview will sink the file. Since that ruling, the statutory bar has been raised further toward spontaneous, detailed expression, so preparation with a proper diploma or test at the right level is essential.<\/p>\n Alongside language, the administration examines civic knowledge through a dedicated civic examination (examen civique): the official service-public.fr pages explain that to be naturalised you must demonstrate assimilation including sufficient knowledge of French history, culture and society, assessed during this examination, and that it applies to acquisition by decree (naturalisation and reintegration) while declaration procedures such as marriage are not concerned (service-public.fr, civic examination<\/a>). Professional integration also counts in practice: stable, declared work and tax compliance in France strengthen the file, while long unemployment without explanation, undisclosed work or tax arrears weaken it. The prefecture conducts an inquiry (enqu\u00eate) covering residence, conduct and loyalty, and the file then goes to the ministry, which decides by decree published in the Journal officiel.<\/p>\n For a British citizen married to a French national, the marriage route (acquisition par d\u00e9claration \u00e0 raison du mariage) is usually faster and more predictable than naturalisation, because it works by declaration rather than discretionary grant. The Code states: “L’\u00e9tranger ou apatride qui contracte mariage avec un conjoint de nationalit\u00e9 fran\u00e7aise peut, apr\u00e8s un d\u00e9lai de quatre ans \u00e0 compter du mariage, acqu\u00e9rir la nationalit\u00e9 fran\u00e7aise par d\u00e9claration \u00e0 condition qu’\u00e0 la date de cette d\u00e9claration la communaut\u00e9 de vie tant affective que mat\u00e9rielle n’ait pas cess\u00e9 entre les \u00e9poux depuis le mariage et que le conjoint fran\u00e7ais ait conserv\u00e9 sa nationalit\u00e9.” (article 21-2 of the Civil Code<\/a>). Four years of marriage is therefore the starting point, with two cumulative conditions on the day of the declaration: the shared life, emotional and material (communaut\u00e9 de vie tant affective que mat\u00e9rielle), must never have stopped since the wedding, and the French spouse must still be French.<\/p>\n The same article extends the waiting period to five years in two situations: where the foreign spouse cannot show three years of uninterrupted regular residence in France since the marriage, or cannot show that the French spouse was registered abroad on the register of French nationals established outside France during their shared life. It also requires prior transcription (transcription) onto French civil-status registers of a marriage celebrated abroad, and sufficient knowledge of the French language assessed under conditions set by decree in Conseil d’Etat. For a British couple married in England before moving to France, the transcription step is often the forgotten one: without it, the declaration cannot proceed.<\/p>\n Declarations based on marriage are received by the administrative authority, which issues a receipt (r\u00e9c\u00e9piss\u00e9) once the documents proving admissibility are supplied: “Les d\u00e9clarations de nationalit\u00e9 souscrites en raison soit du mariage avec un conjoint fran\u00e7ais, en application de l’article 21-2 , soit de la qualit\u00e9 d’ascendant de Fran\u00e7ais, en application de l’article 21-13-1 , soit de la qualit\u00e9 de fr\u00e8re ou s\u0153ur de Fran\u00e7ais, en application de l’article 21-13-2, sont re\u00e7ues par l’autorit\u00e9 administrative.” Secondly: “Il en est d\u00e9livr\u00e9 r\u00e9c\u00e9piss\u00e9 apr\u00e8s remise des pi\u00e8ces n\u00e9cessaires \u00e0 la preuve de leur recevabilit\u00e9.” (article 26 of the Civil Code<\/a>). Keep that receipt: the two-year period during which the Government may oppose the acquisition runs from it. The official service-public.fr pages confirm the four-year minimum and walk through the situations (married four years or more, spouse French since the wedding day) for declarations by marriage (service-public.fr, declaration by marriage<\/a>).<\/p>\n The administration investigates the reality of the shared life: joint home, joint finances, children, testimony and hearings can all be used, and separation, even without divorce, breaks the communaut\u00e9 de vie and defeats the declaration. Language is checked, though at a lower formal threshold than the decree route. If the file is in order, the declaration is registered (enregistr\u00e9e) and nationality dates from the declaration. Registration can be refused (refus d’enregistrement) where conditions are not met, and that refusal can be contested before the courts.<\/p>\n The distinctive risk of the marriage route is not refusal but opposition: even where the conditions appear met, the Government may block the acquisition by decree in Conseil d’Etat, for unworthiness (indignit\u00e9) or lack of assimilation, other than linguistic, within two years of the receipt: “Le Gouvernement peut s’opposer par d\u00e9cret en Conseil d’Etat, pour indignit\u00e9 ou d\u00e9faut d’assimilation, autre que linguistique, \u00e0 l’acquisition de la nationalit\u00e9 fran\u00e7aise par le conjoint \u00e9tranger dans un d\u00e9lai de deux ans \u00e0 compter de la date du r\u00e9c\u00e9piss\u00e9 pr\u00e9vu au deuxi\u00e8me alin\u00e9a de l’article 26” (article 21-4 of the Civil Code<\/a>). Note the words “autre que linguistique”: a language shortfall alone cannot justify opposition on this ground. If the Government opposes, the person is deemed never to have acquired French nationality, though acts done between the declaration and the opposition decree remain valid.<\/p>\n A very recent Conseil d’Etat ruling shows that opposition decrees receive real judicial scrutiny. A Moroccan spouse who had declared nationality through marriage in July 2022 faced an opposition decree in September 2024 for alleged lack of assimilation. The Conseil d’Etat annulled the decree: “Il ne ressort pas des \u00e9l\u00e9ments vers\u00e9s au dossier par le ministre de l’int\u00e9rieur, en particulier du rapport de synth\u00e8se du 26 septembre 2022 des services de la pr\u00e9fecture de l’Oise charg\u00e9s de l’instruction du dossier et du compte-rendu d’entretien compl\u00e9mentaire du 13 mai 2024, que Mme A… adopte un comportement ou soutient des th\u00e8ses manifestant un rejet des principes essentiels de la R\u00e9publique ou se tient d\u00e9lib\u00e9r\u00e9ment \u00e0 l’\u00e9cart de la communaut\u00e9 nationale. Dans ces conditions, Mme A… est fond\u00e9e \u00e0 soutenir que le Premier ministre a fait une inexacte application de l’article 21-4 du code civil en s’opposant, pour d\u00e9faut d’assimilation, \u00e0 ce qu’elle acqui\u00e8re la nationalit\u00e9 fran\u00e7aise.” The operative part follows: “Le d\u00e9cret du 25 septembre 2024 refusant \u00e0 Mme A… l’acquisition de la nationalit\u00e9 fran\u00e7aise est annul\u00e9.” (CE, 29 May 2026, no. 501856, full text on L\u00e9gifrance<\/a>). For British spouses, the message is that an opposition based on vague file impressions, without evidence of rejection of republican principles or deliberate withdrawal from national life, will not survive review.<\/p>\n On the decree route, the ministry has a graduated set of answers. It may declare the application inadmissible (irrecevable) where a legal condition is missing, as in the language case above; it may adjourn (ajourner) the application, typically for two years, where an obstacle looks temporary such as short residence, unstable employment or recent arrival; or it may reject (rejeter) it on the merits. Adjournment is not a polite refusal: it sets a clock, and a fresh application before it expires will fail. Inadmissibility and rejection must state their legal and factual grounds, and that statement of reasons is the first thing to attack if it is missing or contradictory.<\/p>\n Criminal history can bar the route entirely. The Code excludes anyone convicted of crimes or offences against the fundamental interests of the Nation or terrorism, anyone sentenced, for any offence, to six months’ imprisonment or more without suspension, anyone under an unlifted expulsion order or an unexecuted ban from French territory, and anyone whose stay is irregular: “Nul ne peut acqu\u00e9rir la nationalit\u00e9 fran\u00e7aise ou \u00eatre r\u00e9int\u00e9gr\u00e9 dans cette nationalit\u00e9 s’il a \u00e9t\u00e9 l’objet soit d’une condamnation pour crimes ou d\u00e9lits constituant une atteinte aux int\u00e9r\u00eats fondamentaux de la Nation ou un acte de terrorisme, soit, quelle que soit l’infraction consid\u00e9r\u00e9e, s’il a \u00e9t\u00e9 condamn\u00e9 \u00e0 une peine \u00e9gale ou sup\u00e9rieure \u00e0 six mois d’emprisonnement, non assortie d’une mesure de sursis.” (article 21-27 of the Civil Code<\/a>). British applicants with an old UK conviction should therefore take advice before filing: a spent conviction under English law may still appear relevant to the French administration, while rehabilitation or removal from bulletin no. 2 of the criminal record can neutralise it. Do not hide it: concealment is worse than the conviction.<\/p>\n Concealment leads to the gravest outcome, withdrawal of a granted decree. The Code allows decrees of acquisition, naturalisation or reintegration to be withdrawn on the conforming opinion (avis conforme) of the Conseil d’Etat within two years of publication in the Journal officiel where the legal conditions were not met, and within two years of discovery of the fraud where the decision was obtained by lie or fraud: “Les d\u00e9crets portant acquisition, naturalisation ou r\u00e9int\u00e9gration peuvent \u00eatre rapport\u00e9s sur avis conforme du Conseil d’Etat dans le d\u00e9lai de deux ans \u00e0 compter de leur publication au Journal officiel si le requ\u00e9rant ne satisfait pas aux conditions l\u00e9gales ; si la d\u00e9cision a \u00e9t\u00e9 obtenue par mensonge ou fraude, ces d\u00e9crets peuvent \u00eatre rapport\u00e9s dans le d\u00e9lai de deux ans \u00e0 partir de la d\u00e9couverte de la fraude.” (article 27-2 of the Civil Code<\/a>). The Conseil d’Etat has applied this strictly: in one case, a man naturalised in June 2018 was withdrawn in June 2020 after the prefect revealed an undisclosed Algerian marriage and two children, because “le Premier ministre a rapport\u00e9 le d\u00e9cret du 7 juin 2018 pronon\u00e7ant la naturalisation de M. A… au motif qu’il avait \u00e9t\u00e9 pris au vu d’informations mensong\u00e8res d\u00e9livr\u00e9es par l’int\u00e9ress\u00e9 quant \u00e0 sa situation familiale” (CE, 3 February 2022, no. 443462, full text on L\u00e9gifrance<\/a>). The practical rule is absolute: declare every marriage, child, address and conviction, and update the file in writing if anything changes during the procedure. You undertake to do so when you sign, and the administration will check.<\/p>\n Remedies depend on which decision you face. Against a refusal, adjournment or inadmissibility on the decree route, first use the administrative appeal to the minister (recours gracieux or hi\u00e9rarchique review), which is compulsory before going to court and often the fastest way to correct a file error such as a misread language certificate. If that fails, challenge the decision before the administrative tribunal within two months of notification, asking the judge to annul it and order re-examination; the judge reviews legal error, faulty reasoning and manifest error of assessment, as the Nantes language ruling demonstrates. Against an opposition decree on the marriage route, the remedy runs directly to the Conseil d’Etat by action for excess of power (recours pour exc\u00e8s de pouvoir), as the May 2026 annulment shows: the court re-examines whether the file truly establishes unworthiness or non-assimilation. Against a refusal to register a marriage declaration, the dispute goes to the courts for a ruling on whether the statutory conditions were met. In every case, keep the decision letter, the receipt, the interview report and every supporting document: nationality litigation is won on the file.<\/p>\n British applicants should also keep their residence position clean while the nationality file runs. If you are still on the residence side of the process, the visa and permit logic has been mapped in the desk’s hub guide for newcomers, which explains which long-stay visa and which carte de s\u00e9jour a British citizen needs and how to challenge a refusal or removal order<\/a>. An irregular stay during the procedure triggers the article 21-27 bar and destroys both the residence file and the nationality file at once.<\/p>\n The question every British applicant asks first has a reassuring answer on the UK side. The British government confirms that dual citizenship, also known as dual nationality, is allowed in the United Kingdom, so a person can be a British citizen and at the same time a citizen of other countries, and that no application for dual citizenship is needed: applying for a foreign citizenship does not mean giving up British citizenship (GOV.UK, Dual citizenship<\/a>). Becoming French therefore costs you nothing in London: no application, no permission, no loss. France likewise raises no obstacle to a newly naturalised Briton keeping a British passport; French law attaches no loss of French nationality to the mere retention of a prior citizenship acquired at birth. Check the position only if you hold a third nationality whose state forbids duality, which is a matter for that state’s consulate, as GOV.UK itself advises.<\/p>\n Travel becomes simpler, but use the right document at each border. Once French, you are an EU citizen: cross Schengen borders and enter France on your French passport or national identity card, and use the EU lanes. Keep using your British passport for entry to the United Kingdom, where it proves your right of abode without time limit. Do not present yourself as a third-country visitor on arrival in France: as a French national you are not subject to the 90\/180-day Schengen cap, to entry-exit stamping or to a future travel authorisation for your own country, and offering a British passport first can create needless confusion. Carry both documents when crossing the Channel and show each where it belongs.<\/p>\n Your Withdrawal Agreement residence card (carte de s\u00e9jour accord de retrait) becomes redundant once you are French, since an EU citizen needs no residence permit in their own Member State. There is no penalty for holding it during the transition, but renewals, travel-document complications and employer checks all disappear the day you can prove French nationality with a passport, identity card or certificate of French nationality (certificat de nationalit\u00e9 fran\u00e7aise). Notify the prefecture rather than letting files drift, and update your status with your employer, bank and health fund where nationality was recorded.<\/p>\nB. Declaration of nationality after four years of marriage to a French spouse<\/h3>\n
II. Refusals, opposition and dual nationality: protecting your position<\/h2>\n
A. When the administration says no: inadmissibility, adjournment, opposition and how to challenge them<\/h3>\n
B. Keeping your British passport: dual nationality, travel and daily life after you become French<\/h3>\n