You live in Lyon, Bordeaux or a village in the Dordogne, you open your laptop each morning, and you work all day for a company based in Manchester, Leeds or London that has no office, no branch and no subsidiary in France. Since Brexit, this everyday situation sits at the crossing of two complete legal systems: French tax residence against British payroll, and French social security against British National Insurance. The question British remote workers ask — whether having an employer in the UK means paying tax and social charges there — usually gets the opposite answer once the worker’s chair, bed and family are in France. France taxes the salary because the work is physically done in France, and France insures the worker because French law covers everyone who works on its soil, whatever their nationality and whatever country signs their payslip. The employer’s lack of a French establishment changes nothing: a British company employing someone in France must register in France, declare the wages in France and pay French contributions, or face back assessments, criminal exposure for undeclared work and the refusal of the worker’s residence paperwork. This article explains, with the exact texts and the latest court decisions, how tax residence is decided, which country taxes the salary under the Franco-British treaty, which social security system applies, what a UK employer without a French office must concretely do, and how to challenge a tax bill or a social security assessment step by step.

I. Your French home office usually makes you a French tax resident, and France taxes the salary

The first battle is about who you are for tax purposes. If France considers you a French tax resident, it taxes your worldwide income, including the full salary paid from London. If the Franco-British treaty then confirms that residence, the salary for work physically done in France is taxable in France, with Britain giving relief rather than taking the first bite. Both stages follow written rules and a tie-breaker order that no inspector may rearrange.

A. Are you a French tax resident? The home test comes first

French domestic law defines tax residence — the domicile fiscal, meaning the country whose tax system treats you as one of its own residents — through three alternative tests, and meeting any single one is enough. Article 4 A of the Code général des impôts (the French tax code) states the consequence in one sentence: “Les personnes qui ont en France leur domicile fiscal sont passibles de l’impôt sur le revenu en raison de l’ensemble de leurs revenus. Celles dont le domicile fiscal est situé hors de France sont passibles de cet impôt en raison de leurs seuls revenus de source française.” In plain terms, a French tax resident pays French income tax — the impôt sur le revenu — on worldwide income, while a non-resident pays only on French-source income. Article 4 B of the same code then lists the three tests: “Sont considérées comme ayant leur domicile fiscal en France au sens de l’article 4 A : a. Les personnes qui ont en France leur foyer ou le lieu de leur séjour principal ;” — the foyer being your home, the place where you normally live with your family — “b. Celles qui exercent en France une activité professionnelle, salariée ou non, à moins qu’elles ne justifient que cette activité y est exercée à titre accessoire ;” A British employee who rents or owns a flat in France, whose partner and children live there, and who performs every working day from a desk in France will normally satisfy the first test through the family home and the second through full-time professional activity, with neither being merely incidental.

The Conseil d’État — France’s highest administrative court, which decides tax disputes at the final level — reads the home test strictly in the administration’s favour. In a residence dispute decided on 9 June 2021, it recalled the settled definition: “le foyer s’entend du lieu où le contribuable habite normalement et a le centre de ses intérêts familiaux, sans qu’il soit tenu compte des séjours effectués temporairement ailleurs en raison des nécessités de la profession” (Conseil d’État, 9th chamber, 9 June 2021, no. 431551). In other words, the home means where you normally live and keep the centre of your family interests, ignoring temporary stays elsewhere for work reasons. Occasional trips to the London office do not move your home; they are precisely the temporary professional stays the definition disregards. In that same judgment, the court approved judges who had treated a taxpayer as French-resident because his wife lived in France, he paid the local housing tax for her flat, he gave a French address on his identity card and he had no family ties in the other country — a checklist every British remote worker with a family in France should read twice (Conseil d’État, 9 June 2021, no. 431551).

Being treated as resident by both countries does not mean double tax; it triggers the treaty’s tie-breaker. The double tax treaty signed in London on 19 June 2008 and published in France by decree no. 2010-20 of 7 January 2010 provides that the expression resident of a Contracting State covers any person who, under the law of that State, is liable to tax there by reason of domicile, residence, place of management, place of registration or any other similar criterion (treaty of 19 June 2008, Article 4, paragraph 1). Where both countries claim the worker, the treaty imposes a strict order: that person is deemed to be a resident only of the State where she has a permanent home; if she has a permanent home in both States, she is deemed to be a resident only of the State with which her personal and economic relations are closest (the centre of vital interests) (treaty of 19 June 2008, Article 4, paragraph 2, a)). Only if no permanent home exists in either country does the analysis move to habitual presence, then nationality, then mutual agreement between the authorities (treaty of 19 June 2008, Article 4, paragraph 2, b) to d)). For the typical remote worker — a settled home in France, daily life in France, perhaps a rented room used during London visits — the cascade stops at the first step: France, the country of the permanent home. The companion analysis of dual residence under the same treaty, with worked examples of the permanent-home and vital-interests tests, is set out in the treaty-residence guide on this site (British dual tax residence after Brexit: the France-UK tie-breaker).

B. Which country taxes your UK salary? France, where the work is actually done

Once French residence is established, the treaty allocates the salary to the country where the employment is exercised — which, for a home office in France, is France. Article 15 of the treaty, headed “Revenus d’emploi” (employment income), provides: salaries, wages and other similar remuneration derived by a resident of a Contracting State in respect of an employment are taxable only in that State unless the employment is exercised in the other Contracting State, in which case the remuneration for it is taxable in that other State (treaty of 19 June 2008, Article 15, paragraph 1). A French-resident Briton whose laptop never leaves France therefore has a France-taxable salary from the first euro, even though the employer sits in Britain and the contract is governed by English law. Britain then relieves the double taxation through a credit, so the same pounds are not taxed twice in full — but France takes the lead, and the worker declares the wages on the French return, not only on the British one.

The much-discussed 183-day exception does not save the full-time French home worker, because its three conditions apply together and the first already fails. The treaty continues: remuneration for employment exercised in the other State remains taxable only in the State of residence if three cumulative conditions hold: the worker stays in the other State for no more than 183 days in any twelve-month period, the pay comes from an employer who is not a resident of that other State, and the cost is not borne by a permanent establishment the employer has there (treaty of 19 June 2008, Article 15, paragraph 2). Someone who lives and works in France year-round spends far more than 183 days there, so condition (a) collapses immediately; the exception is designed for short missions, not for a permanent remote base. The exception can still matter at the margins: for a worker who genuinely splits time and spends, say, two days a week in the London office over a full year, each block of UK workdays must be measured against the 183-day ceiling, and the payslips, travel records and office badge logs become the evidence that decides which slice each country may tax.

French social levies follow the salary into the French net. Readers are sometimes told that the CSG and CRDS — the contribution sociale généralisée and the contribution pour le remboursement de la dette sociale, two proportional levies collected with income tax on most earnings — are somehow outside tax treaties. For this treaty they are inside it: the French tax administration’s official commentary states that for France the treaty covers income tax, corporation tax, the social contribution on corporation tax, payroll tax, the CSG and the CRDS (BOI-INT-CVB-GBR-10-10, paragraphs 10 and 20). A British remote worker affiliated in France therefore pays CSG and CRDS on the salary under the same treaty umbrella as income tax, and any claim that these levies should be refunded because the employer is British misunderstands the text: the treaty expressly lists them among the French taxes it covers.

II. Your social security follows your work: France insures you, and your UK employer pays there

Tax is only half the bill. Social security — health cover, pensions, family benefits, workplace accidents — obeys its own coordination rules, and since 1 January 2021 those rules between Britain and the European Union come from the Trade and Cooperation Agreement rather than from European Union membership. The architecture is simple to state and demanding to apply: one worker, one applicable legislation at a time, normally the legislation of the country where the work is physically performed. A British national working from France is therefore, as a rule, insured in France and paid for in France, with British detachment as a narrow, time-limited way out.

A. French cover as the rule, British posting as the narrow exception

French law starts from near-universal compulsory cover. Article L. 311-2 of the Code de la sécurité sociale (the social security code) provides: “Sont affiliées obligatoirement aux assurances sociales du régime général, quel que soit leur âge et même si elles sont titulaires d’une pension, toutes les personnes quelle que soit leur nationalité, de l’un ou de l’autre sexe, salariées ou travaillant à quelque titre ou en quelque lieu que ce soit, pour un ou plusieurs employeurs et quels que soient le montant et la nature de leur rémunération, la forme, la nature ou la validité de leur contrat ou la nature de leur statut.” Nationality is irrelevant, the employer’s address is irrelevant, and even the validity of the contract is irrelevant: working in France means belonging to the French general scheme. The French liaison body for international social security, the Cleiss — the official centre that explains which country’s system applies — confirms the cross-border principle survived Brexit: a worker moving within the Union must be subject to a single social security legislation, as a rule that of the State where the work is performed, and that principle was preserved between the United Kingdom and EU Member States including France under the Trade and Cooperation Agreement (Cleiss, employer established in the United Kingdom sending an employee to France). One legislation at a time, normally the country of work: for the home office in France, that is France.

The only standard escape is posting — the détachement, meaning a temporary assignment abroad during which the worker stays under the home country’s system. The Cleiss sets out the post-Brexit terms precisely: posting allows a worker sent on a temporary assignment in France to stay under the British social security system for a maximum of 24 months, where the conditions are met (Cleiss, UK employer page). Two conditions must both hold: the worker must not be sent to replace another posted worker, and the planned mission must not exceed 24 months — and the page adds, in bold, that there is no way around the ceiling: no extension and no exceptional derogation are possible (Cleiss, UK employer page). Where posting is granted, the British institution issues an A1 form certifying that the worker stays under the British system for the duration of the assignment (Cleiss, UK employer page), the portable document the worker keeps and shows at any French inspection. Where posting is refused, the same page is blunt: social contributions for that worker are then obligatorily due in France at French rates. A permanent remote job from France is not a temporary mission, so it cannot qualify; the A1 route serves genuine short assignments, not a settled home office. British guidance mirrors the logic from the other side of the Channel, warning that National Insurance may still be payable in the UK while working abroad, and a worker who stays under British cover needs a certificate of coverage showing that National Insurance is paid in the UK and that no social security contributions are due in the country of work (GOV.UK, National Insurance if you work abroad). No certificate, no British cover: French contributions apply.

The Cour de cassation — France’s highest civil and criminal court — confirmed the mirror image of this reasoning in 2022 for French workers sent abroad: where no international convention or regulation keeps them under French law, “les travailleurs détachés temporairement à l’étranger par leur employeur pour y exercer une activité salariée ou assimilée, rémunérée par cet employeur, sont soumis à la législation française de sécurité sociale à la condition que l’employeur s’engage à s’acquitter de l’intégralité des cotisations dues auprès de la caisse d’affiliation du salarié” (Cour de cassation, 2nd civil chamber, 13 October 2022, no. 21-13.252). The structure is symmetrical: international coordination first, and failing that, the legislation of the country of employment with the employer paying the full contributions to the worker’s fund. For the British remote worker in France, the coordination instrument is the Trade and Cooperation Agreement’s social security protocol, and its answer is the same as the Cleiss gives: absent valid posting, France insures and France collects.

B. A UK employer with no French office must still register, declare and pay — or face the courts

Having no French establishment — no office, no branch, in French terms no établissement — excuses nothing. The Cleiss puts the duty plainly: a foreign employer with no pre-existing establishment in France must register in France (Cleiss, UK employer page). Registration runs through the dedicated national service of the contribution-collection network, the Urssaf — the body that collects social contributions — and its Foreign Firms department, with supplementary pension going to the designated institution: the page points to the “Urssaf – Service Firmes Étrangères” for general-scheme contributions and to Malakoff Humanis International Agirc-Arrco for compulsory supplementary retirement (Cleiss, UK employer page). Once registered, the British employer declares the wages, issues French-compliant payslips — the bulletins de paie — and pays employer and employee contributions at French rates, exactly as a French company would. Genuine posting is different from permanent remote work and obeys its own statute: Article L. 1262-1 of the Code du travail (the labour code) allows a foreign employer to post workers to France only temporarily, “à condition qu’il existe un contrat de travail entre cet employeur et le salarié et que leur relation de travail subsiste pendant la période de détachement”, and only within three defined frameworks, including work under a contract with a French-based recipient or between establishments of the same group. A settled home office with no French client, no French establishment and no return date fits none of these boxes.

Immigration paperwork follows the same logic and must be arranged before work starts. A British citizen who needs a work-based residence status for an open-ended contract falls under the employee card: Article L. 421-1 of the Ceseda (the French immigration code) provides that “L’étranger qui exerce une activité salariée sous contrat de travail à durée indéterminée se voit délivrer une carte de séjour temporaire portant la mention ” salarié ” d’une durée maximale d’un an”, and that “La délivrance de cette carte de séjour est subordonnée à la détention préalable d’une autorisation de travail” — the carte de séjour being the residence permit and the autorisation de travail the work authorisation. The practical sequence is fixed by the administration, which states that the employer must make the request for work authorization, and only once it is granted can the worker apply for the long-stay visa that serves as a residence permit (Service-public.fr, working in France: salarié residence card). A British employer that has never hired in France must therefore organise the work authorisation through the official online channel before the first payslip, not after the first inspection. Withdrawal Agreement beneficiaries who already hold a residence card with the right to work are in a different, easier position, but the newly arrived remote worker has no shortcut.

An employer that skips registration, declarations or payslips enters the criminal law of undeclared work — the travail dissimulé. Article L. 8221-5 of the labour code deems it concealed employment for any employer who deliberately avoids the hiring declaration — the déclaration préalable à l’embauche — provided for by Article L. 1221-10, avoids issuing a payslip, or “se soustraire intentionnellement aux déclarations relatives aux salaires ou aux cotisations sociales assises sur ceux-ci auprès des organismes de recouvrement des contributions” — deliberately avoids wage and contribution declarations to the collection bodies. The offence requires intent, but intent is routinely inferred from a complete absence of paperwork: no registration, no declarations and no payslips over months of full-time work leave little room for the oversight defence. On top of criminal exposure, the Urssaf raises back assessments — the redressements — for all contributions avoided, and the amounts for a full-time salary quickly reach tens of thousands of euros before surcharges.

Waving a British-issued A1 certificate does not automatically end the argument. Three criminal chamber rulings map the exact boundary. Where the issuing institution was never asked to reconsider, a French court may not simply brush the certificate aside: the court quashed a conviction entered without checking “si l’institution portugaise émettrice desdits certificats avait été saisie d’une demande de réexamen et de retrait à la lumière d’éléments établissant une fraude et s’était abstenue de les prendre en compte” (Cour de cassation, criminal chamber, 12 January 2021, no. 18-86.757). But where the French body did seek review with evidence gathered in a criminal investigation and the issuer ignored it, the trial court may set the certificates aside where, “dans le respect des garanties inhérentes au droit à un procès équitable qui doivent être accordées à ces personnes, il constate l’existence d’une telle fraude” (Cour de cassation, criminal chamber, 12 January 2021, no. 17-82.553). The most recent word, from June 2026, sharpens the test: where the issuing institution confirms certificates “sans se prononcer sur les éléments concrets soumis par l’institution compétente de l’État membre d’accueil qui donnent à penser que ces certificats ont été obtenus ou invoqués de manière frauduleuse”, that confirmation “ne peut être assimilé à un réexamen effectif”, and the court of the host country that finds fraud “peut les écarter” (Cour de cassation, criminal chamber, 9 June 2026, no. 24-85.090). For a sham posting — a certificate covering what is really a permanent French home office — the French judge therefore has a mapped path to disregard the paper, provided the dialogue procedure with the British institution was genuinely attempted first. The practical lesson for employers is to keep posting certificates for genuine short missions only, and to register for French contributions everywhere else.

When the assessment or the refusal arrives, the challenge follows a fixed two-stage route with strict time limits. Social security litigation — the contentieux de la sécurité sociale — covers, by statute, “les litiges relatifs : 1° A l’application des législations et réglementations de sécurité sociale” (Article L. 142-1 of the social security code), and court action in these matters “sont précédés d’un recours préalable” — a prior appeal — under conditions set by decree (Article L. 142-4 of the same code). In practice that prior appeal goes to the friendly-appeal commission — the commission de recours amiable — and the deadline for submitting a complaint to the CMRA is 2 months from the date of notification of the decision being challenged (Service-public.fr, disputing a social security decision). If the commission rejects the complaint or stays silent, the worker or employer then has a second two-month window: a request must then be addressed to the judicial court (social pole) or sent by registered letter with acknowledgement of receipt within 2 months: from the date of notification of the CMRA decision being challenged or, in the absence of a response from the CMRA, from the expiry of the 4-month period available to it to respond to the complaint (Service-public.fr, disputing a social security decision). The judicial court in question — the tribunal judiciaire, sitting in its social division — is the court of the worker’s home, so a remote worker living in Paris brings the case before the Paris court, with payslips, the employment contract, A1 documents, travel records and the commission’s file as the core bundle. Miss either two-month deadline and the assessment becomes final regardless of its merits, which is why the notification date on every Urssaf letter must be diary-recorded on arrival.

Conclusion

The British remote worker living in France for a British employer is, in the eyes of French law, a French taxpayer insured in France whose employer happens to sit across the Channel. Tax residence follows the family home and the daily professional activity under Article 4 B, the treaty tie-breaker confirms France through the permanent home, and Article 15 gives France the salary because the employment is exercised there. Social security follows the same geography: French affiliation as the rule, twenty-four-month British posting without extension as the narrow exception proved by an A1, and registration with the Urssaf foreign-firms service wherever the work is really permanent. Each link in that chain is written in a verifiable text and policed by courts that have recently shown they will set aside sham certificates after a genuine review attempt. Workers should therefore align their declarations with their real life — French return, French affiliation, preserved travel evidence — and employers should register before the inspector calls, because the back assessment, the contribution surcharges and the concealed-work prosecution all cost more than compliance. Done properly, the cross-Channel home office is perfectly lawful; it is simply French for tax and social security purposes, whatever flag flies over the employer’s letterhead.