Since 1 January 2021, British citizens have been third-country nationals in France. The Withdrawal Agreement protected those already settled, and the long-stay visa route remains open to newcomers, but neither gives you a French passport. For many Britons who have rebuilt their lives in France, naturalisation by decree (naturalisation par décret) is now the decisive step: it secures the right to stay without renewing a residence permit, opens full political rights, simplifies travel, and settles the question for children born in France. This guide explains, for a British reader, how French citizenship by decree works after Brexit, whether you can keep your British passport, what the language and assimilation interview really tests, and how to challenge a refusal, an adjournment or an endless delay. Every decisive statement below is anchored in the Civil Code (Code civil), the 1993 decree on nationality decisions, recent judgments of the Conseil d’État and the Nantes courts, and the official pages of the French administration and GOV.UK.
I. Can a British citizen living in France become French after Brexit and keep both passports?
A. How long must you live in France before applying for French citizenship?
The basic rule is five years of habitual, lawful residence. Article 21-17 of the Civil Code provides 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”, subject only to the exceptions in articles 21-18, 21-19 and 21-20. A second, separate condition sits in article 21-16: “Nul ne peut être naturalisé s’il n’a en France sa résidence au moment de la signature du décret de naturalisation.” In plain terms, you must have lived in France for the five years before you apply, and you must still be living there when the decree is signed. Leaving France for good while the file is pending can therefore destroy the application, even if everything else is perfect.
For Britons, the Brexit calendar matters enormously here. Years spent in France under EU mobility rules before 2021 count, provided the residence was genuine and habitual. The holder of a Withdrawal Agreement residence permit (often called the WARP card) who arrived in 2018 and applies in 2026 plainly satisfies the five-year stage. By contrast, time spent hopping across the Channel as a visitor under the 90-days-in-180 rule does not build a résidence habituelle: short stays in a second home, however regular, are not settlement. Nor does unlawful residence help, and the criminal-record bar discussed below expressly excludes anyone in that position: article 21-27 of the Civil Code covers “celui dont le séjour en France est irrégulier au regard des lois et conventions relatives au séjour des étrangers en France”. If you moved after Brexit on a long-stay visa (visa de long séjour valant titre de séjour) and then renewed a carte de séjour each year, your five-year clock started when you actually settled, not when you bought the house or first dreamed of the move. Students should note a trap hidden in the case law: years of residence as a student can count toward the stage, but a file showing no professional insertion after graduation regularly ends in rejection, as the Conseil d’État case law on resources and insertion below demonstrates.
Three groups of Britons can apply sooner. First, article 21-18 of the Civil Code reduces the stage to two years for a foreigner who has “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”, for a person who has rendered or can render great services to France, and for a foreigner showing “un parcours exceptionnel d’intégration” in civic, scientific, economic, cultural or sporting life. A British graduate of a French university, a researcher recruited by a French laboratory, or an entrepreneur whose business created significant French employment should examine this shortcut closely rather than waiting out five full years. Second, the spouse of a French citizen has a different route altogether: article 21-2 of the Civil Code allows a foreigner married to a French spouse to “après un délai de quatre ans à compter du mariage, acquérir la nationalité française par déclaration”, provided the shared life, emotional and material, has continued without break and the French spouse has kept French nationality. The period rises to five years where the foreign spouse cannot show three years of uninterrupted lawful residence in France since the wedding. A British woman married to a Frenchman in London, living with him in Paris since 2022, would therefore typically declare in 2026; a marriage celebrated abroad must first have been transcribed onto the French civil-status registers (transcription sur les registres de l’état civil français), a formality couples often discover late. Third, refugees and certain protected persons benefit from exemption from the stage under article 21-19, which matters for the rare British file involving asylum, but not for the mainstream British applicant.
Practical evidence of the five years must be assembled like a court bundle, because the préfecture (préfecture, the local office of the State administration that receives the file) checks continuity, not highlights. Tax notices (avis d’imposition), yearly residence permits, employment contracts and payslips, proof of address for each year, and school certificates for children together draw an unbroken line. Gaps invite questions: a year back in Britain caring for an elderly parent, even for sympathetic reasons, can break habitual residence if France ceased to be the centre of your life. Keep every récépissé (the receipt the administration issues when a complete file is lodged), every permit, and every tax assessment. The file that proves five quiet years of French life beats the file that merely asserts them.
B. Do you lose your British passport if you become French?
No. This is the fear that stops more British applications than any legal obstacle, and it is unfounded in both directions. On the British side, the GOV.UK guidance on dual citizenship confirms that the United Kingdom accepts dual nationality, so applying for French nationality costs you nothing on the British side and no separate application for dual status is needed Becoming French does not strip you of British citizenship, you do not need to apply for permission to be a dual national, and the Home Office expects dual nationals to exist. On the French side, France has tolerated dual nationality (double nationalité or pluralité de nationalités) for decades: the Civil Code nowhere requires a naturalised person to renounce their former citizenship, and the naturalisation decree does not ask for proof of renunciation. A British applicant who takes the oath and signs the charter of rights and duties of the French citizen (charte des droits et devoirs du citoyen français) wakes up the next morning holding two nationalities and able to renew either passport.
Two practical consequences of dual nationality deserve attention before you apply. First, diplomatic protection stops at the border of the second citizenship. The same GOV.UK guidance warns that British-French dual nationals cannot call on UK diplomatic help while on French soil. If you are arrested, hospitalised or caught in a crisis in France, Britain treats you as French first; conversely, France treats you as British first when you are in the United Kingdom. For most daily life this changes nothing, but travellers who assumed the consulate would always intervene should adjust their expectations. Second, travel documents must be used consistently. A dual national can travel to the United Kingdom on either a valid British passport or a certificate of entitlement, and cannot obtain an Electronic Travel Authorisation as a British dual citizen; entering France, show the French identity card or passport to avoid awkward questions about the purpose and duration of your stay. Families should apply the same logic to children: a child born in France to a newly naturalised British parent may already be French by birth on French soil or may need a declaration, and the parents should check the child’s status rather than assuming one passport covers everyone.
One related question returns constantly in British households: does the British spouse who does not apply gain anything from the other’s naturalisation? The answer is indirect but real. A French citizen’s foreign spouse can use the four-year declaration route of article 21-2 described above, which is simpler and faster than the decree route, with no discretionary judgment on the opportunity of the grant. A British couple where one spouse qualifies a year earlier than the other sometimes plans the two applications in sequence: decree first for the longer-settled spouse, then declaration by marriage for the partner. The marriage must be genuine and the shared life continuous, and marriages celebrated in England must be transcribed onto the French registers first, but for many couples this sequencing halves the waiting time. Children, for their part, benefit through the effet collectif (the collective effect by which the minor children of a naturalised parent, habitually resident with that parent, become French automatically), provided they live with the naturalised parent and their names appear in the decree. Check the decree when it arrives: a child omitted from it is not covered, and a separate declaration may be needed.
A final Brexit-specific reassurance: naturalisation does not depend on the Withdrawal Agreement, and the Agreement does not cap the number of Britons who may become French. Some clients worry that applying for French citizenship somehow betrays or abandons their protected status under the Agreement. It does not. The Agreement froze residence rights as they stood; citizenship adds a second layer of security on top. Others fear that a failed application endangers their residence permit. It does not either: the naturalisation service and the residence-permit service apply different rules, and article 21-15 of the Civil Code frames naturalisation as exactly what it says, “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” — a favour requested, whose refusal leaves existing rights intact. The genuine risks of the procedure lie elsewhere: in the language test, the resources test, the criminal-record bar, and delay. Those are the subject of Part II.
II. How do you apply for French naturalisation and what if the prefect says no?
A. What does the language and assimilation interview actually test?
French law makes assimilation (assimilation à la communauté française) the gateway condition. Article 21-24 of the Civil Code, in its version in force since 1 January 2026, opens bluntly: “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.” The statute then describes the expected command of French in demanding terms: the applicant must show a level allowing at least “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”. Readers familiar with the Common European Framework will recognise upper-intermediate proficiency here, well above holiday French. “A l’issue du contrôle de son assimilation, l’intéressé signe la charte des droits et devoirs du citoyen français”, the charter recalling the principles, values and symbols of the Republic. Britons who passed the old, lighter test years ago should therefore recalibrate: the bar has risen, and the file must prove a level of French that survives a real conversation about abstract subjects, not merely the vocabulary of shopping and school runs.
In practice the check has two limbs: a certificate and an interview. Most applicants must produce a diploma or attestation proving the required level, and then face the individual assimilation interview (entretien d’assimilation) at the préfecture or on the online platform, where an agent tests spoken French and knowledge of French history, culture, society and civic values. A judgment of the Nantes appeal court shows exactly how the interview is judged and how hard it is to overturn. In CAA Nantes, 2 April 2020, no. 19NT04015, a Syrian applicant challenged a refusal based on insufficient French. The court recalled the implementing rule then in force: “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.” The evaluation grid (grille d’évaluation) attached to the interview report had been properly used, the applicant had been unable to understand the essential points of an ordinary conversation, and “L’évaluateur a conclu que le niveau B1 requis n’était pas atteint.” Personal testimonials from relatives that she managed daily errands alone could not outweigh the official report, and the court concluded that “eu égard au large pouvoir dont il dispose, le ministre a pu, sans commettre d’erreur de fait ou d’erreur d’appréciation, déclarer irrecevable la demande de naturalisation de Mme F… pour défaut d’assimilation linguistique”. Three lessons for British applicants follow. First, the interview report (compte-rendu d’entretien) is the decisive document: prepare for it as an examination, not a chat. Second, private certificates and friendly attestations weigh little against a poor interview. Third, the minister enjoys broad discretion (large pouvoir d’appréciation), and the judge reviews only for factual error or manifest misjudgment, a light-touch control that upholds most refusals. Note the historical detail: that 2020 case applied the former B1 threshold. Under the 2026 wording quoted above, the required proficiency is materially higher, so a Briton whose French stopped progressing after the move should invest in structured courses and a recognised test well before filing.
Assimilation is not only language. The agent also probes knowledge of French institutions, history and values, and adhesion to republican principles: laïcité (secularism in public life), equality between women and men, and acceptance of the laws of the Republic. Polygamy, forced marriage, or a demonstrated rejection of core values can justify refusal on this ground. Professional and social insertion counts too, through the resources test examined by the Conseil d’État. In CE, 29 November 2019, no. 421050, the high court restated the framework: “L’autorité administrative dispose, en matière de naturalisation ou de réintégration dans la nationalité française, d’un large pouvoir d’appréciation.” It may weigh “l’intégration de l’intéressé dans la société française, son insertion sociale et professionnelle et le fait qu’il dispose de ressources lui permettant de subvenir durablement à ses besoins en France”. The applicant in that case lived essentially on social benefits, and the court upheld the refusal. But it also drew a protective line that matters for elderly or disabled British residents: “l’autorité administrative ne peut se fonder ni sur l’existence d’une maladie ou d’un handicap ni, par suite, sur l’insuffisance des ressources de l’intéressé lorsqu’elle résulte directement d’une maladie ou d’un handicap”. A British retiree in the Dordogne living on a modest but stable UK state and private pension, topped up lawfully, presents durable resources of a different nature than dependence on subsistence benefits; a younger applicant with years of undeclared cash work and no tax record presents the opposite picture. Declare your worldwide income in France, keep continuous employment or credible self-employment evidence, and show that your household durably meets its needs: the file must read as insertion, not survival.
The criminal-record bar is mechanical and unforgiving. Article 21-27 of the Civil Code excludes anyone convicted of crimes against the fundamental interests of the Nation or terrorism, and, whatever the offence, anyone “condamné à une peine égale ou supérieure à six mois d’emprisonnement, non assortie d’une mesure de sursis”. Expulsion orders, bans from French territory, and irregular residence trigger the same exclusion. British applicants sometimes assume a spent English conviction, an old caution, or a motoring endorsement is invisible to the French administration. It may not be: the enquiry runs through French records and declared history, and concealment itself destroys credibility. There is, however, one precise escape route, confirmed by the Conseil d’État. In CE, 21 December 2021, no. 447231, the court held that the 21-27 bar “ne trouvent pas à s’appliquer à l’étranger condamné qui a bénéficié d’une réhabilitation de plein droit dans les conditions énoncées par l’article 133-13 du code pénal”, rehabilitation acquired automatically after the statutory period without a new criminal conviction. It added that “La circonstance que la condamnation n’aurait pas été effacée du bulletin n° 2, comme le prévoit le 5° de l’article 775 du code de procédure pénale, est sans incidence à cet égard” — the lingering mention on bulletin no. 2 of the criminal record does not revive the bar once legal rehabilitation has operated. A Briton with a single old custodial sentence, followed by decades of clean life, should therefore take advice on whether rehabilitation has wiped the obstacle before letting the prefecture declare the file inadmissible; conversely, a recent suspended sentence revoked for reoffending, as the administration alleged in that very case, leaves the bar firmly in place. Check the record early, never hide it, and build the timeline with a lawyer if the past is complicated.
B. How do you challenge a refusal, an adjournment or an endless delay before the Nantes court?
Refusals come in three legal shapes, and the remedy depends on identifying the right one. The prefect or the minister can declare the application inadmissible (irrecevabilité: a statutory condition is missing, such as the five-year stage or the language level), reject it (rejet: the conditions are met but the administration, using its broad discretion, considers the grant inopportune, for example for weak insertion or insufficient resources), or adjourn it (ajournement: the decision is postponed, typically for two years, imposing a waiting period or conditions such as stabilising employment or completing language training). The power to adjourn comes from article 48 of decree no. 93-1362 of 30 December 1993, in the wording recalled by the Conseil d’État in the 421050 judgment: “Si le ministre chargé des naturalisations estime qu’il n’y a pas lieu d’accorder la naturalisation ou la réintégration sollicitée, il prononce le rejet de la demande. Il peut également prononcer l’ajournement en imposant un délai ou des conditions”. An adjournment is not a refusal, but it feels like one; its advantage is that it tells you exactly what to fix. A rejection for poor insertion after a short, patchy work history calls for two years of stable payslips and tax returns before reapplying. An adjournment conditional on language progress calls for a recognised diploma at the required level. Read the reasons (motifs) first, react second: every decision must state the factual and legal grounds, and the grounds dictate the strategy.
Time limits protect the applicant against administrative silence. Article 21-25-1 of the Civil Code sets the clock: “La réponse de l’autorité publique à une demande d’acquisition de la nationalité française par naturalisation doit intervenir au plus tard dix-huit mois à compter de la remise de toutes les pièces nécessaires à la constitution d’un dossier complet contre laquelle un récépissé est délivré immédiatement.” The period falls to twelve months for a foreigner showing ten years of habitual residence in France at the date the complete file is lodged, and both periods “peuvent être prolongés une fois, par décision motivée, pour une période de trois mois”. Keep the receipt proving when the complete file was lodged: without it, the eighteen-month clock arguably never started. If the administration stays silent beyond the deadline, or issues a refusal, the applicant has two stages of challenge. The official English-language page of the French administration, service-public.fr on naturalisation by decree, explains that an application to the minister before going to court is optional, so you may go directly to court, but a hierarchical appeal (recours hiérarchique or recours gracieux to the minister) is often tactically wise: it costs nothing, it sometimes corrects a clear file-reading error, and it resets the clock for the judge. Where that appeal fails, the same page states the rule for online and postal files alike: silence for four months after your appeal counts as a refusal, and a two-month window then opens to bring the case before the court in Nantes.
That court is the same for every applicant in France. Article R312-18 of the Code of Administrative Justice provides that “le tribunal administratif de Nantes est compétent pour connaître des recours dirigés contre les décisions du ministre chargé des naturalisations”. A British resident of Bordeaux, Lyon or Paris therefore litigates in Nantes, usually through a lawyer, and the appeal from Nantes goes to the Nantes administrative court of appeal, with the Conseil d’État as final judge. One procedural subtlety, confirmed by the Nantes appeal court in its 2 April 2020 judgment, regularly catches applicants out: “les décisions par lesquelles le ministre statue sur les recours préalables obligatoires se substituent à celles des autorités préfectorales qui lui sont déférées”. The minister’s decision on the prior appeal replaces the prefect’s decision, so the court action must target the minister’s decision as it stands at the date of the hearing, not the original prefectural letter. Aim at the wrong decision and the claim is dismissed as inadmissible without any examination of the merits.
Before the judge, expectations must be realistic about the standard of review. Naturalisation by decree is a favour (faveur), not a right: where the statutory conditions are satisfied, the administration may still refuse if it considers the grant inopportune, and the judge annuls only for legal error, factual inaccuracy, or manifest error of assessment (erreur manifeste d’appréciation). The three judgments used in this guide map the terrain. The 2020 Nantes language case shows refusals upheld where the interview report documents failure against the evaluation grid. The 2019 Conseil d’État resources case shows refusals upheld where benefits-dependent resources reveal weak insertion, while protecting applicants whose low income flows directly from illness or disability. The 2021 Conseil d’État rehabilitation case shows the administration losing where it misread the criminal-record bar against a rehabilitated applicant. The winning strategies follow from this map: attack inadmissibility decisions on the facts (prove the stage, the level, the rehabilitation with documents), attack rejections by showing the assessment rested on a material error (wrong income figure, ignored stable employment, confusion between two offences), and treat adjournments as timetables rather than verdicts. New facts beat new adjectives: a fresh diploma, twelve months of payslips, or proof of rehabilitation moves a file further than ten pages of indignation. Where the refusal followed a genuinely failed interview, reapplying after real progress routinely succeeds where litigating the old interview fails. Where the file was strong and the reasoning thin or mistaken, the Nantes court can annul and order reconsideration within a fixed period, as the appeal court did before the Conseil d’État confirmed the rehabilitation analysis in 2021.
Two final Brexit-era pitfalls deserve a warning. First, some British applicants let their residence permit lapse while waiting for the nationality decision, assuming the pending file protects them. It does not: until the decree is signed, you remain a foreign national subject to residence-permit rules, and article 21-27 excludes applicants in irregular residence. Renew the carte de séjour on time, every time, until the Journal officiel publishes your name. Second, travel during the procedure should stay reasonable. The administration verifies that residence remains habitual until signature under article 21-16; a six-month return to Britain mid-procedure, however justified by family reasons, invites an adjournment or a fresh enquiry. Notify changes of address, answer every request for documents within the deadline, and keep copies of everything sent. The naturalisation file is a two-year relationship with the administration, and files handled with the discipline of a court case reach the decree; files handled casually reach the adjournment.
Conclusion
French citizenship by decree is open to every British resident who makes France the lasting centre of life: five years of habitual lawful residence, or two for graduates of French higher education and exceptional profiles, or four years of marriage to a French spouse by declaration. The United Kingdom allows you to keep your British passport, France asks for no renunciation, and the children’s status can be settled in the same decree. The real selection happens on assimilation in its post-2026, more demanding form, on durable resources proving genuine insertion, and on a clean or rehabilitated record, with eighteen months as the administration’s answer deadline and the Nantes administrative court as the single judge of refusals. Prepare the language like an examination, document five years like a trial bundle, renew the residence permit until the decree is signed, and challenge a wrong decision within its two-month window rather than letting it harden. Done this way, the British applicant stops being a former European citizen on a renewable permit and becomes what the procedure promises: a French citizen who also happens to be British.
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