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HMRC letter codes · National Insurance (CA)

CA8421Certificate for working in several countries

Last reviewed 14 October 2026 · How Tax Letters checks its facts

In short

GOV.UK lists the CA8421 as the form to apply for a certificate confirming you pay UK National Insurance when working in 2 or more countries.

“Apply for a certificate to confirm you pay UK National Insurance when working in 2 or more countries (CA8421)”

GOV.UK: Apply for a certificate to confirm you pay UK National Insurance when working in 2 or more countries (CA8421) · checked 14 October 2026

Information, not advice: this page reports what HMRC, GOV.UK and the bodies named publish about CA8421. Each fact has its source and the day it was checked beside it.

What it asks

GOV.UK's CA8421 page says you will need your country and place of birth, and which nationalities you hold.

“you’ll need the following information: … your country and place of birth … which nationalities you hold”

GOV.UK: Apply for a certificate to confirm you pay UK National Insurance when working in 2 or more countries (CA8421) · checked 14 October 2026

GOV.UK's CA8421 page says an agent's client needs to fill in an authorising your agent (64-8) form, and the completed form is submitted with the CA8421 application form.

“your client needs to fill in an authorising your agent (64-8) form. You should submit the completed form with your CA8421 application form.”

GOV.UK: Apply for a certificate to confirm you pay UK National Insurance when working in 2 or more countries (CA8421) · checked 14 October 2026

Time limits and rules

GOV.UK’s CA8421 page says the form is for people living in the UK and working in 2 or more countries in the UK, EU, Gibraltar, Iceland, Liechtenstein, Norway or Switzerland, and for flight or cabin crew whose home base is in the UK, among others.

“Use this form if you: … are living in the UK, and working in 2 or more countries in the UK, EU, Gibraltar, Iceland, Liechtenstein, Norway or Switzerland … are working as a flight or cabin crew member, where your home base is in the UK”

GOV.UK: Apply for a certificate to confirm you pay UK National Insurance when working in 2 or more countries (CA8421) · checked 14 October 2026

How to send it or apply

GOV.UK's CA8421 page says you apply online by signing in (creating sign in details if you do not have them), and that you can save your answers and return later.

“You’ll need to sign in to use this service. If you do not already have sign in details, you’ll be able to create them. … You do not have to fill in the form in one go. You can save your answers and return later.”

GOV.UK: Apply for a certificate to confirm you pay UK National Insurance when working in 2 or more countries (CA8421) · checked 14 October 2026

Free help and HMRC contacts

If you have a question about a certificate of coverage, such as one about CA8421, GOV.UK’s National Insurance enquiries page says to call HMRC on 0300 200 3500. Lines are open Monday to Friday, 8am to 6pm, and the page links to “Find out about call charges”.

“Call HMRC for help and information with: … certificate of coverage (also known as a PDA1 or A1) queries … Telephone: 0300 200 3500 … Opening times: Monday to Friday, 8am to 6pm. … Find out about call charges”

GOV.UK: National Insurance: enquiries · checked 14 October 2026

Free help first

These routes are described by GOV.UK, TaxAid and Citizens Advice themselves.

  • HMRC's extra supportHMRC offers extra support if your health condition or personal circumstances make it difficult to contact HMRC, for example a mental health condition, financial hardship or being treated in hospital.
  • Someone to deal with HMRC for youYou can authorise a friend, relative or voluntary organisation to talk to HMRC for you and help you fill in forms.
  • TaxAidTaxAid helps people with tax problems who cannot pay for advice. Tax Help for Older People merged with TaxAid in July 2025.
  • Citizens AdviceCitizens Advice gives confidential advice online, over the phone and in person, for free.