You live in France, your employment contract is with a company in London, and your working day happens at a desk in Lyon, Bordeaux or Paris. Every month, your British employer runs a British payroll, deducts British income tax under PAYE and British National Insurance, and sends you a payslip in pounds. Then the French administration knocks: the tax office wants your worldwide salary declared in France, and URSSAF, the French social-security collection body, wants employer and employee contributions on that same salary, plus penalties for never having registered the employment in France. Since Brexit, this collision has become routine, and it is expensive. This guide explains, for a British citizen resident in France and working remotely for a British employer, where the salary is taxed, which country’s social security applies, what your employer must do in France, and how to challenge a tax bill or a URSSAF reassessment.
I. Your salary is paid from London but your life is in France: where is it taxed?
A. Are you a French tax resident, and what does the France-UK treaty tie-break decide?
The first question is always residence, because residence decides which country taxes your worldwide income. French domestic law treats you as fiscally domiciled in France when your home, your principal place of stay, your professional activity or the centre of your economic interests is in France; these are alternative tests, so meeting any one of them is enough. Living year-round in France with your family home there will normally satisfy at least two of them at once. French social-security law itself points to this definition when it provides that “Les personnes physiques fiscalement domiciliées en France au sens de l’article 4 B du code général des impôts sont assujetties à une contribution sur les revenus du patrimoine assise sur le montant net retenu pour l’établissement de l’impôt sur le revenu” (article L. 136-6 du code de la sécurité sociale, version en vigueur). In plain terms, once France regards you as its tax resident, it claims your salary wherever the employer sits, and it also reaches associated levies on your capital income.
Because the United Kingdom may claim you too, especially in the year of the move, the double tax treaty signed in London on 19 June 2008 and published in France by decree No 2010-20 of 7 January 2010 settles the conflict. Article 4 first lets each country apply its own domestic residence test, covering liability based on domicile, residence, place of management, place of registration or any similar criterion. Where both countries claim you, the treaty imposes a tie-break with a strict order. The first step is the permanent home, known as the “foyer d’habitation permanent”: if you have one in each country, residence goes to the state of your closest personal and economic ties, the “centre des intérêts vitaux”. Only if that centre cannot be determined does the treaty look at habitual stay, then nationality, then mutual agreement between the tax authorities. For a British remote worker whose family, house and daily life are in France, the tie-break usually confirms French residence, and the treaty commentary published by the French tax administration at BOFiP, France-UK treaty section follows the same logic.
That conclusion has an immediate practical consequence. As a French resident, you must declare your worldwide employment income on the French annual return, convert sterling amounts at the rate applicable for the year, and report the British tax already withheld so that the treaty credit mechanism can operate. Failing to declare because “my employer already taxed me in London” is the single most common and most costly mistake: the French administration treats an undeclared foreign salary as concealed income, with penalties and interest running from the original deadline. Keep every P60, every payslip and every P45 from the year of departure, because the French inspector will ask for them, and the exchange of information between HMRC and the French tax administration means the salary is rarely unknown to Paris. If you arrived during the year, organise the split of pre-arrival and post-arrival income from day one, with tenancy agreements, travel records and utility bills proving when your permanent home moved.
When the assessment arrives and you disagree with it, the challenge route is a formal claim to the tax office, followed by an appeal to the administrative court if the claim is rejected expressly or by silence. The claim must identify the tax, the year and the legal ground: treaty residence under Article 4, correct application of the employment article, or correct computation of the credit. Time limits are short, generally 31 December of the second year following the year of the disputed assessment for income tax, so a bill received in autumn must be answered before the year-end clock runs out. Attach the treaty, the decree publishing it, the payslips and proof of British tax paid; a bare letter saying “I was taxed in the UK” achieves nothing. Where the dispute turns on dual residence, ask the French administration to engage the mutual agreement procedure with HMRC rather than letting each country tax the full salary while you wait.
B. London payroll, French work: how Article 15 divides the salary and how France gives credit
Once residence is settled, Article 15 of the treaty allocates the right to tax employment income, and its starting point surprises many remote workers. The rule is that salaries and similar employment income are taxable only in the residence state unless the employment is performed in the other state, in which case the income becomes “imposables dans cet autre Etat”. If you are resident in France and you physically perform the work in France, France is the state where the employment is exercised, so France has the primary right to tax the salary, even though the contract is English, the employer is British and the money is paid into a British bank account. The place of actual performance controls, not the employer’s address and not the payroll location.
Article 15 then provides a narrow exception, and remote workers should read its three conditions carefully because they almost never help a permanent remote arrangement. Salary for work performed in the other state can remain taxable only at home if three cumulative conditions are all met: presence in the other state not exceeding 183 days in any twelve-month period, payment by or for an employer not resident in that other state, and remuneration not borne by a permanent establishment the employer has there. A British employee living full-time in France fails the logic of the exception from the start, because the exception protects short missions into the other state, not a home office that has become the normal place of work. Days spent visiting the London office do not change the analysis for the rest of the year: each portion of salary follows where the corresponding duties were performed, so keep a work diary distinguishing days worked in France from days worked in Britain.
Because the United Kingdom may still operate PAYE on the full salary while France taxes it as the state of performance, the treaty eliminates the resulting double charge through a credit on the French side. The mechanism gives the French resident a “crédit d’impôt imputable” against French tax, subject to the treaty’s conditions and limits, with a ceiling equal to the French tax attributable to that income. In practice, you declare the gross British salary in France, compute French tax on it, then offset the British tax paid within that ceiling. The excess, where British tax exceeds French tax on the same income, is not refunded by France, which is why asking the British employer to operate a reduced PAYE code or to move you to a French-compliant payroll matters as much as the return itself. Discuss with a payroll adviser whether your circumstances allow HMRC to exclude French-workdays from PAYE, and never stop UK withholding unilaterally on the strength of your own treaty reading.
Two traps deserve emphasis. The first is the social levies: as a French tax resident affiliated to a French scheme, your salary also bears French employee charges and the employer owes French employer charges, which no treaty credit absorbs, because the treaty covers taxes, not social contributions. The second is the calendar: a mid-year arrival can make you UK-resident for the British tax year that runs to 5 April and French-resident from arrival, so one salary can fall into two different reporting years and the credit must be claimed in the right one on each side. Reconcile the two calendars line by line before filing, and if the French office denies the credit for lack of proof of British payment, supply the P60 and the HMRC employment history rather than resubmitting the same claim unchanged.
II. Which country’s social security covers work performed in France, and what must your British employer do?
A. Work performed in France is insured in France: affiliation, payroll duties and the concealed-work risk
Social security follows the place of work, and French statute states the rule in the widest possible terms: “Sous réserve des traités et accords internationaux régulièrement ratifiés ou approuvés et des règlements européens, sont affiliées à un régime obligatoire de sécurité sociale dans le cadre du présent code, quel que soit leur lieu de résidence, toutes les personnes : 1° Qui exercent sur le territoire français : a) Une activité pour le compte d’un ou de plusieurs employeurs, ayant ou non un établissement en France ; b) Une activité professionnelle non salariée” (article L. 111-2-2 du code de la sécurité sociale, version en vigueur). The phrase “ayant ou non un établissement en France” is the key: a London company with no office, no branch and no subsidiary in France that employs someone working from a French home still triggers French affiliation. There is no de minimis exception for one employee, no remote-work exception and no tolerance period during which British National Insurance alone would suffice for activity performed on French soil.
The courts enforce this territoriality strictly against foreign employers. In a 2025 ruling concerning a Portuguese company, where “à la suite d’un contrôle portant sur la période du 1er janvier 2010 au 30 septembre 2013 au titre des infractions aux interdictions de travail dissimulé mentionnées à l’article L. 8222-1 du code du travail, l’URSSAF a adressé à la société [3] (la société), le 19 mars 2015, une lettre d’observations portant redressement suivie, le 23 décembre 2015, d’une mise en demeure” (Cour de cassation, deuxième chambre civile, 16 octobre 2025, pourvoi n° K 23-14.039, published in the Bulletin), the appeal court had annulled the reassessment on the ground that URSSAF inspectors could not demand detachment documents from a company with no French presence. The Court of Cassation quashed that reasoning and confirmed that approved and sworn inspectors verify the employer’s declarations by collecting any documents, whatever their form, that show whether the foreign-seated employer is affiliated in France. The message for a British employer is direct: URSSAF inspectors may demand proof of French affiliation from a company with no French presence, and defeating the control on jurisdictional grounds will not survive cassation.
The boundary disputes run in both directions, which confirms that affiliation follows work and not wishes. In another 2025 decision, a woman “domiciliée en France et travaillant en Suisse” had asked URSSAF for “le remboursement des cotisations versées depuis 2015 au titre de son affiliation à l’assurance maladie en France” (Cour de cassation, deuxième chambre civile, 25 septembre 2025, pourvoi n° F 22-24.634). The litigation tested exactly where contributions were due when residence and workplace straddle a border, and it shows that neither paying voluntarily in the wrong country nor holding strong convictions about the right one protects you: the only question is where the work is performed and which coordination instrument, if any, displaces the territorial rule. Since Brexit, no EU regulation covers a British employer and a French home worker as a matter of course; the Withdrawal Agreement protects acquired positions, and the EU-UK Trade and Cooperation Agreement contains a social-security protocol, but a routine new remote arrangement starts from French affiliation unless a certificate of continued British coverage has actually been issued.
French affiliation imposes concrete employer duties from the first day of work. Hiring requires that “L’embauche d’un salarié ne peut intervenir qu’après déclaration nominative accomplie par l’employeur auprès des organismes de protection sociale désignés à cet effet.” (article L. 1221-10 du code du travail, version en vigueur), the prior declaration known as the DPAE. Each payday requires that “Lors du paiement du salaire, l’employeur remet aux personnes mentionnées à l’article L. 3243-1 une pièce justificative dite bulletin de paie.” (article L. 3243-2 du code du travail, version en vigueur), a payslip meeting French content rules, not merely the British one. Contributions are then due to URSSAF on the French base, and a foreign employer with no French establishment registers with the dedicated URSSAF service for foreign firms, which functions as its French collection counterpart. Skipping these steps converts a payroll oversight into an offence: “Est réputé travail dissimulé par dissimulation d’emploi salarié le fait pour tout employeur : 1° Soit de se soustraire intentionnellement à l’accomplissement de la formalité prévue à l’article L. 1221-10”, which covers the prior hiring declaration, (article L. 8221-5 du code du travail, version en vigueur), with back contributions, surcharges and possible criminal exposure. A British employer that discovers the omission should regularise spontaneously before any control, because voluntary disclosure weighs heavily in the negotiation of surcharges.
From the British side, the position mirrors the French one: the UK government guidance on working abroad warns that British contributions may continue during a posting and that a certificate of coverage may be needed to prove it (GOV.UK, National Insurance if you work abroad). The same page describes a 52-week continuation for employees “working abroad temporarily”. A permanent move to France fails the temporary condition, so the 52-week continuation does not cover a settled French home worker, and double contributions for at least an initial period are a real cash-flow risk until the payroll is reorganised. The certificate of coverage, where available under the applicable agreement, is the document that prevents that doubling, so apply for it before the move rather than after the first URSSAF letter.
B. Detached is not remote: contract status, accidents, certificates and how to challenge a reassessment
British employers often reach for the wrong label, calling the arrangement a posting or secondment, in French a détachement, when it is in fact permanent remote work. The statute defines detachment narrowly: “Un employeur établi hors de France peut détacher temporairement des salariés sur le territoire national, 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.” (article L. 1262-1 du code du travail, version en vigueur). Temporarily is doing the work in that sentence: detachment covers a mission with an end date, after which the employee returns, whereas a British employee who has relocated the family home to France and works there indefinitely is not on a mission. The Court of Cassation illustrated the difference in a 2023 case where “M. [B] a été engagé par la société Leonardo Finmeccanica, établie à [Localité 4] (Italie), le 12 octobre 1979” and “Il a été détaché, en France, auprès du GIE ATR, à compter du 1er juillet 1995”, before the employer ended the posting and ordered a return to Italy, which the employee contested as an abuse of detachment (Cour de cassation, chambre sociale, 5 avril 2023, pourvoi n° F 21-21.318). Detachment has a beginning, an end and a return; remote work has a home office and no return date. Misclassifying a permanent remote worker as detached invites URSSAF to recharacterise the whole period and bill the contributions with surcharges.
The correct framework for the arrangement is remote work, télétravail, which French law defines as follows: “le télétravail désigne toute forme d’organisation du travail dans laquelle un travail qui aurait également pu être exécuté dans les locaux de l’employeur est effectué par un salarié hors de ces locaux de façon volontaire en utilisant les technologies de l’information et de la communication.” (article L. 1222-9 du code du travail, version en vigueur). The same article guarantees that “Le télétravailleur a les mêmes droits que le salarié qui exécute son travail dans les locaux de l’entreprise.” (article L. 1222-9 du code du travail, version en vigueur). Remote status therefore changes nothing about employment protection: working from France for London does not make you a contractor, does not remove dismissal rules and does not allow the employer to ignore French working-time, health-and-safety and equipment obligations. If the reality is subordinate employment performed from France, re-labelling it as freelancing changes the risk from a payroll adjustment to a reclassification claim with years of back contributions, so choose the status that matches the facts and document it.
Accidents are the point where remote workers discover affiliation most painfully. French law provides that “L’accident survenu sur le lieu où est exercé le télétravail pendant l’exercice de l’activité professionnelle du télétravailleur est présumé être un accident de travail” (article L. 1222-9 du code du travail, version en vigueur), a presumption measured against the general definition of work accidents. The underlying definition is that “Est considéré comme accident du travail, quelle qu’en soit la cause, l’accident survenu par le fait ou à l’occasion du travail à toute personne mentionnée à l’article L. 311-2.” (article L. 411-1 du code de la sécurité sociale, version en vigueur). A fall down the stairs of the French house between two video calls is therefore presumed to be a work accident where French affiliation exists, and the British employer’s UK employer’s-liability policy rarely covers it. Declare the home workplace to the French occupational-accident insurer, keep the remote-work agreement or charter required by Article L. 1222-9 on file, and ensure the payslip funds the corresponding contributions; otherwise the injured worker faces a coverage gap and the employer faces liability for uninsured risk.
For readers in Paris and the Île-de-France, two practical points strengthen the file. First, the competent collection body is URSSAF Île-de-France and the competent court for contribution disputes is the social chamber of the Paris judicial court, so correspondence, payment references and deadlines must be directed there, not to a British payroll bureau. Second, Parisian salaries make the stakes higher: employer charges in France commonly add roughly four-tenths on top of gross salary, so a £90,000 London salary performed entirely from Paris can generate a reassessment well into six figures in euros once three years of contributions, surcharges and late interest are aggregated. Budget the exposure before URSSAF does it for you, and consider whether the employer should engage a French payroll provider or an employer of record while keeping the British contract under review for applicable-law and jurisdiction clauses.
When the reassessment letter arrives, act in the statutory order and within the deadlines printed on the document. Start with the amicable appeal to the URSSAF appeals commission, setting out each ground separately: wrong affiliation period, days actually worked outside France, erroneous base, duplicate British contributions covered by a certificate, or misapplied surcharge rate. If the commission confirms the bill, appeal to the social chamber of the judicial court, where the 2025 rulings cited above show judges examining the employer’s declarations and the place of actual work document by document. Preserve the work diary, badge and travel records, the remote-work agreement, the DPAE once filed, the French payslips, the British P60s and any coverage certificate; the party that proves where each working day happened usually wins the affiliation argument. Where the non-working partner has no professional income, remember that French universal cover may bill a separate annual contribution, a point developed in our guide on British early retirees facing the French PUMA charge, and where the arrangement might genuinely become independent work, compare with our analysis of British freelancers and the auto-entrepreneur route before choosing that status.
Conclusion
Living in France while working remotely for a British employer after Brexit means accepting two cumulative logics: France taxes the salary because the work is performed there, and France insures it for the same reason. The treaty tie-break in Article 4 will normally confirm your French residence, Article 15 will allocate the salary to France as the state of performance with a credit for British tax rather than an exemption, and Article L. 111-2-2 will affiliate you to the French scheme even though your employer has no French establishment. The employer’s duties follow automatically: prior declaration, French-compliant payslip, registration with the foreign-firms service and contributions to URSSAF, with detachment available only for genuine temporary missions and remote-work rules governing the home office, including the work-accident presumption. The 2025 Court of Cassation rulings confirm that URSSAF controls of foreign employers are valid and that affiliation disputes are decided on the facts of where work happened. Organise the proof now, work diary, travel records, payslips on both sides and coverage certificate, regularise before the control where possible, and challenge any bill ground by ground through the amicable commission and then the court. A remote arrangement set up correctly costs contributions but buys legal certainty; one left on a London-only payroll buys a reassessment.