Guides / Naturalisation

Naturalisation applications (form AN)

What the online application to naturalise as a British citizen asks for, where firms lose time preparing it, and how Aion fills it from the client's documents. Written for immigration solicitors and IAA-registered advisers.

Last updated: 15 October 2026

The application at a glance

• How to apply: online on gov.uk, from inside the UK. The applicant then books a UK Visa and Citizenship Application Services (UKVCAS) appointment to give fingerprints and a photo. Documents are uploaded or scanned at the appointment, not posted (gov.uk).
• Settled status: the applicant must usually have held indefinite leave to remain or settled status for 12 months. This does not apply if they are married to, or the civil partner of, a British citizen.
• Residence: in the UK on the date exactly 5 years before the Home Office receives the application, with no more than 450 days outside the UK in those 5 years and no more than 90 days in the last 12 months. For the spouse or civil partner of a British citizen, the period is 3 years, with no more than 270 days outside the UK in those 3 years and 90 days in the last 12 months (Form AN guidance).
• Other requirements: aged 18 or over, English at the required level, a Life in the UK Test pass, good character, and an intention to keep living in the UK (gov.uk).

What the application asks for

The paper Form AN and its guidance set out what the application asks for. It covers:

• Identity: names used, date and place of birth, nationality, passports, and details of the applicant's settled status (eVisa, BRP or grant letter).
• Residence and absences: every period spent outside the UK in the residence period, with dates. gov.uk asks for as much detail as possible about time abroad.
• Good character: criminal convictions in the UK and abroad, and other questions about conduct and immigration history.
• Knowledge of English and life in the UK: the Life in the UK Test reference and the English evidence, or the reason for an exemption.
• Parents: each parent's full name (and the mother's name before marriage), town and country of birth, nationality and date of birth.
• Spouse or civil partner: for the 3-year route, evidence that they are a British citizen.
• Referees: the application must be endorsed by two referees who have each known the applicant for at least 3 years. One can be of any nationality but must be a professional person. The other must hold a British citizen passport and be either a professional person or over 25. Neither can be related to the applicant or to each other, be the applicant's solicitor or agent on this application, or work for the Home Office, and the Home Office will not usually accept a referee convicted of an imprisonable offence in the last 10 years.
• Future intentions: confirmation that the applicant intends to keep living in the UK.

Where firms lose time

Five years of absences

The 450-day and 90-day limits are easy to state and slow to check. Every trip has to be listed and totalled, usually from the client's own records checked against passport stamps. Clients often forget short trips, and the totals have to be right for both windows.

Dates that must agree with the ILR grant

The settled status date, the 12-month wait and the start of the residence period all have to line up with the Home Office's own records. Gathering old grant letters and BRPs to confirm them takes time.

Good character disclosures

The character questions are broad. Firms have to draw out anything the client might need to disclose and decide how to present it, before any of it goes into the form.

Referee details

Referee names, addresses, occupations, nationality and how long they have known the applicant all need collecting and checking against the rules on who can act. A referee who turns out to be ineligible, such as a relative of the other referee, has to be replaced before the application goes in.

How Aion handles a naturalisation application

1. Start an application in Aion, choose naturalisation, and add your firm's representative details.
2. Upload the client's documents: passports, the ILR grant or eVisa record, the Life in the UK pass, English evidence, marriage certificate where relevant, your travel schedule and your questionnaire with referee details.
3. Aion extracts names, dates, reference numbers, addresses, absences and family details into one summary.
4. Your caseworker checks and edits that summary, including every trip abroad, before anything is filled. The original documents are deleted as soon as extraction succeeds.
5. Aion fills the gov.uk application in a live browser your team can watch, and stops at the Declaration page with a report of anything missing or uncertain.
6. Your team reviews the whole application and submits it. Aion never submits.

What stays with your firm

• Advice on eligibility, including absences over the limits and whether to ask for discretion.
• Judgements on good character and how to disclose anything relevant.
• Choosing suitable referees, submitting the application, paying the fee and booking biometrics.

Worried about putting client data into an AI tool? Read Is it safe to use AI for UK visa applications? and our security summary.

Sources: gov.uk: Apply for citizenship if you have ILR · gov.uk: How to apply · gov.uk: Becoming a British citizen · Form AN guidance · Form AN (02/26). Requirements change. Check gov.uk and the Home Office guidance before relying on any figure here.