Moving from the United Kingdom to France often produces a practical tax problem before it produces a tax bill: you are asked for a French tax number, yet you have never filed a French return and cannot create an online account. The French numéro fiscal is the personal tax identification number used by the tax administration. It is not a visa, a residence permit, a French social-security number or proof that you have become French tax resident. A British citizen can need one as a French resident, or because French-source income must be declared while the person remains non-resident.

Brexit does not remove the need to establish the correct French position. It changes the immigration and some administrative context, but the French domestic residence tests and the France–UK double-tax treaty still govern the tax analysis. The first practical objective is therefore not to guess a number or repeatedly retry FranceConnect, the public online identity service. It is to build a clear file showing where you live, which income is concerned, which year is being declared and which French service has jurisdiction. This guide sets out that route, the documents that usually matter, and the remedies available when the tax office refuses to register you, assigns the wrong status or leaves a first return unanswered.

For wider move and split-year context, see our guide to moving from the UK and filing the first French tax return. This narrower article covers the identifier and refusal, so the pages serve different needs.

I. Do I need a French tax number after moving from the UK?

A. Am I tax resident in France after Brexit?

Nationality is not the starting point. The first question is whether French law treats you as having your tax domicile in France, and then whether the treaty allocates residence to France or the United Kingdom if both domestic systems regard you as resident. The French Code général des impôts (CGI, the General Tax Code) states in Article 4 A that persons whose tax domicile is in France are liable to income tax on their entire income, while a person domiciled outside France is liable on French-source income. The key distinction is worldwide income reporting for a French resident, not a special Brexit category.

Article 4 B of the CGI identifies three alternative domestic connections. They are the French household or principal place of stay, a professional activity in France unless it is shown to be merely ancillary, and the centre of economic interests in France. The official text refers to leur foyer ou le lieu de leur séjour principal, to professional activity, and to le centre de leurs intérêts économiques. These are not three cumulative conditions. A strong connection under one criterion can be enough under French domestic law, subject to the treaty rule if the United Kingdom also claims you.

Counting days is useful evidence, but it is not a complete answer. A British person who spends fewer than 183 days in France may still have a French household, employment or economic centre. Conversely, spending substantial time in France does not automatically settle a dual-residence case without looking at the permanent home, family life, work and financial links. Keep a dated chronology: the date the French home became available, the date the UK home was retained or let, travel records, school or family arrangements, employment location and the place where regular expenses are paid.

The treaty signed in London on 19 June 2008 is published in the French Official Journal through the decree publishing the France–UK convention. Its Article 4 deals with residence. If a person is resident in both countries under domestic law, the treaty looks first at a permanent home, then at the closer personal and economic links, described in the French text as the centre des intérêts vitaux. If that cannot decide the issue, habitual abode, nationality and an agreement between the competent authorities follow in sequence. The treaty does not mean that a British citizen can select the more convenient country by preference; it requires evidence applied to the facts.

A recent illustration is the judgment of the Paris Administrative Court of Appeal, seventh chamber, 18 June 2026, no. 23PA05246. The case concerned the tax residence of a person with links to London and France in a French property capital-gains dispute, not the issuing of a tax number. The court examined the household, accommodation, family circumstances, bank activity, utility consumption and work pattern. That is a useful warning for a newly arrived British taxpayer: a lease or a residence card alone may not answer a residence question, and a statement that the UK remains “home” is weaker than a documented chronology.

Residence status also changes what must be declared. A French resident normally reports French and foreign income in the French system, subject to the treaty and the classification of each item. A non-resident may still need to report French employment, rental, pension or other French-source income. The official Service-Public explanation of taxes paid by a foreign national in France is a useful starting point, but it is not a substitute for applying the treaty to a mixed UK–France situation.

Do not treat a French tax number as conclusive evidence of residence. The administration can issue an identifier so that it can process a return or French-source income even where the taxpayer is non-resident. The converse is also true: having a number does not by itself prove that France has taxing rights over every UK pension, salary, dividend or capital gain. The tax number identifies the file; the residence analysis determines the scope of the declaration and the tax treaty relief.

B. When must I obtain a numéro fiscal and file a first return?

A numéro fiscal is generally a thirteen-digit identifier assigned to an individual taxpayer. You may find it on a French tax notice, a previous correspondence from the direction générale des finances publiques (DGFiP, the French public-finance administration), or an account already created on the French tax website. A person who has never been assessed in France will not necessarily have one before making the first declaration. That is the situation in which many British movers are trapped: the online service requests the number, while the number can only be generated after the first paper file is examined.

The official answer from impots.gouv.fr on a first income-tax declaration explains that a first declaration may need to be made on paper. The same page distinguishes people who already have a number from people who have never filed. If you have no identifier, do not invent one, borrow a spouse’s identifier or submit a series of incomplete online forms. The correct request is a written first-registration file sent to the service responsible for the declaration, with the paper return where the tax administration requires it.

The account-creation procedure is described on the official page “How to create my online account”. The page explains that the route is different when the taxpayer has no number. A first paper return and identity documents allow the administration to create the taxpayer record; the number can then be used to activate the online espace Finances publiques, meaning the personal tax account. That sequence matters if a British bank, notary, employer, landlord or social agency asks for an avis d’impôt, the official French tax notice: the notice cannot be downloaded before the underlying file exists.

There are several common scenarios:

• New French resident. You moved your household to France during or before the tax year and must report the relevant French and foreign income. The move date and the split between the two countries should be explained rather than left to an unexplained form entry.
• Non-resident with French-source income. You remain treaty-resident in the UK but receive French rent, work income, a French pension or another French-source item. The tax number may be needed for the non-resident file even though your worldwide income is not declared in France on the same basis.
• Property owner with no prior return. Owning a French home can create local-tax, income-tax or wealth-tax questions, but ownership alone does not settle income-tax residence. The tax number should be requested for the actual obligation, not used to disguise the fact that the person is only a second-home owner.
• Couple or civil partnership. The administration must know whether the first return is individual or concerns a joint French tax household. A spouse’s identifier is not interchangeable with the other spouse’s identifier, and a joint filing position should be supported by the marriage or civil-partnership certificate and the household chronology.
• Move during the year. The first French declaration may contain a period of French residence and a period of UK residence. UK payslips, pension statements, bank interest and rental records should be retained so that the allocation can be explained and the treaty provisions claimed consistently.

Foreign accounts deserve particular care. If you are domiciled or established in France, Article 1649 A of the CGI requires the references of foreign accounts opened, held, used or closed to be declared with the income return, subject to the statutory scope and forms. The official wording includes les références des comptes ouverts, détenus, utilisés ou clos à l’étranger. For a British mover, that may include UK current accounts, savings accounts and certain investment accounts. It is separate from the question whether the underlying interest or gain is taxable in France under the treaty.

The obligation to file is not erased merely because the number has not yet arrived. Article 170 of the CGI, in the official version checked for the first-return rule, requires a person liable to income tax to submit a detailed declaration of income, family circumstances and the elements needed to calculate the tax. The exact form depends on the facts: form 2042 is the main income return, while form 2047 is generally used to report foreign income that must be carried into the French return. Use the current forms and instructions supplied by the tax administration for the year concerned; do not rely on a form downloaded from an old tax year.

For an initial registration, write a short cover letter that says plainly: you are a British citizen, the address and date from which you have lived or earned French-source income, the tax year concerned, the reason you need the number, and whether you believe you are French resident or treaty-resident in the UK. A carefully stated alternative position is better than a contradictory form. If the residence question is genuinely uncertain, say so and identify the facts that require analysis.

II. How do I obtain the number and challenge a refusal?

A. Which documents should I send to the French tax office?

Start by identifying the correct Centre des finances publiques, the public finance centre for the relevant address. For an individual resident in France, the relevant department is usually the service des impôts des particuliers (SIP, individual tax department) for the French home. A person treated as non-resident for the relevant income may instead need the service des impôts des particuliers non-résidents (SIPNR, non-resident individual tax department). The contact route can change according to the type of tax, so use the contact function on impots.gouv.fr and keep a copy of the service result, the date and the postal or electronic address used.

Address the request to the service rather than to a generic British or French embassy mailbox. A consulate can sometimes provide orientation, but it does not create a French tax number. An accountant can prepare calculations, but the DGFiP must register the taxpayer. If the file concerns French rental income, a property sale, a pension or a disputed residence, say so in the subject line so that it is routed to the correct team.

A practical document pack should normally contain the following, adapted to the facts:

• a clear copy of the current passport, showing the identity used on the return;
• the French address and proof of occupation, such as a lease, completion statement, utility bill or accommodation certificate, with the relevant dates;
• the date of arrival, the date the French home became the main household and a concise travel or residence chronology if the year was split;
• the first paper income return and the supporting schedules required by the current instructions, including foreign-income information where applicable;
• evidence of the income concerned: UK employment records, pension statements, bank-interest certificates, rental statements, dividend records or other documents that explain the source and period;
• evidence relevant to treaty residence if the UK position is maintained, such as the UK address, family and work facts, and the UK tax reference or tax correspondence where it helps identify the position;
• marriage, civil-partnership or dependent-child documents when the household or family quotient affects the first return;
• every prior message from the French tax service, including a screenshot or letter showing a failed online registration, and the date of any telephone conversation.

Do not send an unstructured bundle of confidential documents. Label each attachment in English or French, give the tax year, and state what fact it proves. If a UK document is not self-explanatory, add a one-line English explanation and, where the service requests it, a French translation. Do not send original passports or irreplaceable originals by ordinary post. Keep a complete scanned copy and preserve the delivery evidence, including the tracking number and the date the service received the file.

The tax office is entitled to examine declarations and supporting material. Article L.10 of the Livre des procédures fiscales (LPF, the Tax Procedure Book) states that the administration controls declarations and acts used to establish taxes and may request information, justifications or explanations. The official text says L’administration des impôts contrôle les déclarations. A request for documents is therefore not, by itself, evidence of wrongdoing. It is also a reason to submit a coherent, indexed file rather than a bare demand for a number.

Ask the service to confirm four things in writing: whether the file is treated as a resident or non-resident registration; which form or schedule is missing; whether a number has already been assigned under another spelling or address; and which date the declaration is considered received. British names can create duplicate records when a middle name, hyphen or married name is used differently. Check the spelling before sending a second application. A duplicate file can delay the notice and create avoidable correspondence about two addresses.

If the service says that an online account is impossible without a number, quote the first-declaration guidance and ask for the paper route. If it says that a residence permit is required, distinguish the immigration document from the tax record and ask which statutory tax obligation is being processed. A British citizen with a valid basis to declare French-source income should not be left without a filing route merely because the online portal is designed for people who already have an identifier.

Keep the income declaration and the request for an identifier together where possible. The number is a registration tool; it is not a precondition for truthfully disclosing income. If the ordinary filing deadline is approaching, send the return with a cover letter explaining that the number has been requested and that the administration has not yet assigned it. Use a traceable method and retain proof. The exact late-filing consequences depend on the facts and the amount due, but waiting silently can make the position harder to regularise.

B. How do I appeal a refusal or correct my French tax position?

First separate three different problems. A refusal to create or identify a taxpayer record is an administrative registration problem. A notice that calculates the wrong amount is an assessment problem. A disagreement about whether the treaty gives France or the UK the taxing right is a residence or double-tax problem. The same letter can mention all three, but the remedy and deadline may differ. Calling every problem a “tax appeal” can send a first-registration request to the wrong procedure.

For a registration refusal, send a formal written request for review to the service that refused the file. Quote the date, the reference, the documents already sent and the exact practical consequence: inability to file, inability to obtain an assessment notice, inability to declare foreign accounts, or inability to respond to a request. Ask for a written decision and the legal or factual reason for refusal. Attach the complete indexed pack again if the first exchange was by telephone or through an online form that produced no receipt.

Where the issue is an assessment, an omitted credit, an incorrect residence treatment or a tax paid in error, the formal réclamation contentieuse (tax claim seeking correction or repayment) becomes relevant. Article L.190 of the LPF says that claims concerning taxes, contributions, duties, charges and penalties fall within contentious jurisdiction when they seek correction of an error in the basis or calculation of tax, or the benefit of a right under legislation or regulation. The official wording refers to la réparation d’erreurs commises dans l’assiette ou le calcul des impositions. A letter asking only for a number is not automatically a claim against an assessment; a challenge to the resulting tax bill may be.

Deadlines must be calculated from the type of tax and the event that starts the period. Article R*196-1 of the LPF, in the version in force from 30 July 2026, provides the general rule for many taxes: claims are normally filed no later than 31 December of the second year following the relevant collection, payment or event. The text begins Pour être recevables and identifies the date of collection, the payment where there is no assessment notice, or the event giving rise to the claim. Local taxes follow a separate rule under R*196-2. Never copy a deadline from a different type of tax without checking the notice and the current text.

The claim should identify the taxpayer, the tax and year, the notice or payment, the relief sought, the factual chronology, the legal grounds, and the evidence. Article R*197-1 of the LPF states the basic rule that claims are individual. If you are filing for a spouse or another person, prove the authority to act. The administration may require a copy of the assessment or payment evidence, and a claim sent from outside France can trigger a request for a French address for service. Keep a signed PDF, the attachments and evidence of delivery.

Do not confuse a request for treaty relief with a claim that the United Kingdom automatically wins. The France–UK convention allocates different categories of income through different articles. Residence under Article 4 is only the first step; pensions, employment, rent, dividends and capital gains can have their own rules. State the relevant income category and the exact treaty provision relied upon. A UK tax return, HMRC correspondence or a certificate of residence can support the analysis, but none of them replaces the French declaration when France has a domestic filing obligation.

The Conseil d’État decision of 12 February 2020, no. 435907, illustrates why a treaty credit must be tied to the treaty text and the character of the income. The court examined the France–UK convention and stated that the income in issue had to be included in the UK tax base for the relevant credit condition, while effective UK taxation was not necessarily required on the facts described. This is not a ruling that resolves every British pension or investment account. It is a reminder to identify the income, the country’s taxing rule and the precise relief mechanism instead of relying on the general phrase “double taxation agreement”.

A refusal or an incorrect notice should be challenged with a paper trail, not repeated portal attempts. The sequence should normally be:

1. request the written reason and identify the service that made the decision;
2. send a corrected first-registration file or a formal tax claim, depending on whether a notice or payment is being challenged;
3. explain the residence chronology and the treaty article, with one document tied to each material fact;
4. calculate the applicable deadline and send before it expires, even if the service has not answered an earlier informal message;
5. preserve the acknowledgement, delivery evidence and every response;
6. obtain advice promptly if a notice, enforcement action, audit or significant foreign-income correction is already underway.

Late filing has consequences that should be assessed rather than guessed. Article 1728 of the CGI, currently shown on Légifrance as amended on 19 February 2026, provides graduated increases for a declaration filed late: 10% in the ordinary situations described in paragraph 1(a), 40% after a formal demand is not met within the relevant period, and 80% in the concealed-activity situation described by the text. The penalty is calculated by reference to the tax and circumstances; it is not an automatic fixed fine simply because a new British resident asked for a number. A taxpayer who has acted transparently and documented the registration problem is in a better position to request the proper treatment.

The declaration calendar also matters. Article 175 of the CGI contains the statutory framework for the income-return filing date, subject to the annual timetable and electronic or paper rules. The date announced for a particular campaign should be checked on the current official tax instructions. A British taxpayer who moved late in the year should not assume that the first return can wait until a tax number appears, or that a UK filing deadline extends the French deadline.

Where the dispute concerns an active audit or a proposed correction, respond within the deadline in the administration’s letter and distinguish evidence from legal argument. Article L.10 LPF confirms the administration’s power to ask for explanations, while Article L.190 LPF provides the framework for contentious correction once an assessment or payment is at issue. If a notice is issued after the service has refused to register the first return, challenge the notice and the registration history together, without assuming that one procedure suspends the other.

Recent case law can help frame the evidence but should not be overextended. In no. 23PA05246, the Paris court looked closely at the real centre of the taxpayer’s personal and economic life; in no. 435907, the Conseil d’État analysed the conditions for applying a France–UK treaty credit. Neither case creates a universal rule for every British mover. Your dates, family, work, accounts, property use and income documents remain decisive. The right way to use a judgment is to extract the legal test it actually applied, then show how your evidence meets or distinguishes that test.

For a British household in France, the most useful escalation file therefore has five layers: identity; residence chronology; income and account schedules; the French form and tax year; and the correspondence showing the refusal or error. Number the pages and cross-reference each factual assertion. If the administration later asks for clarification, the same file can be updated rather than rebuilt. If the dispute becomes litigation, the chronology and delivery evidence will usually matter as much as the first message requesting a number.

Conclusion

A British citizen does not obtain a French tax number by virtue of Brexit, a visa or ownership of a French home. The identifier follows a French tax record. That record may concern worldwide income because France is the person’s residence state, or French-source income because the person remains resident in the UK under domestic law and the France–UK treaty. Establish the status from evidence, identify the correct SIP or SIPNR, request the number and file the first return on the paper route when the online service cannot accept a new taxpayer.

If the tax office refuses, ask for the reason in writing and separate registration from assessment. If a notice or payment is wrong, use the LPF claim procedure within the applicable deadline, state the treaty provision and attach a document for each material fact. A coherent file sent before the deadline is the practical foundation for obtaining the number, correcting the tax record and avoiding an unnecessary escalation.

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