HMRC letter codes · Self Assessment (SA)
SA1Register for Self Assessment
Last reviewed 14 October 2026 · How Tax Letters checks its facts
In short
GOV.UK's page on registering for Self Assessment says form SA1 is the postal form for people who are not self-employed and cannot register online.
“Register for Self Assessment if you're not self-employed … If you cannot register online … You can register by post. … Fill in form SA1.”
GOV.UK: Check how to register for Self Assessment · checked 14 October 2026
Information, not advice: this page reports what HMRC, GOV.UK and the bodies named publish about SA1. Each fact has its source and the day it was checked beside it.
What it is
GOV.UK's page on registering for Self Assessment names a different postal form for people who are self-employed: form CWF1, as the alternative to SA1.
“Register for Self Assessment if you’re self-employed … You can register by post. … Fill in form CWF1.”
GOV.UK: Check how to register for Self Assessment · checked 14 October 2026
What it asks
GOV.UK says that, for someone who is not self-employed, registering by post with form SA1 means you will need your personal details and information about why you need to complete a tax return.
“You can register by post. You’ll need: your personal details information about why you need to complete a tax return … Fill in form SA1.”
GOV.UK: Check how to register for Self Assessment · checked 14 October 2026
Time limits and rules
GOV.UK says that after you have registered, HMRC will give you a Unique Taxpayer Reference (UTR); if you registered by post, using form SA1, you will usually get your UTR by post in 15 working days (21 days if you are abroad), but it may take longer during busy periods.
“After you’ve registered HMRC will give you a Unique Taxpayer Reference (UTR). … If you registered by post You’ll usually get your UTR by post in 15 working days (21 days if you’re abroad), but it may take longer during busy periods.”
GOV.UK: Check how to register for Self Assessment · checked 14 October 2026
How to send it or apply
GOV.UK says to fill in form SA1, print it and post it to HMRC, using the postal address shown on the form.
“Fill in form SA1. Print and post it to HMRC, using the postal address shown on the form.”
GOV.UK: Check how to register for Self Assessment · checked 14 October 2026
GOV.UK says you can register for Self Assessment online and save your progress to finish later, that you cannot register online if you do not live in the UK, and that form SA1 is the postal option for people who are not self-employed.
“Register online … You can save your progress and come back to finish registering later. … You cannot register online if you do not live in the UK. … Register for Self Assessment if you're not self-employed … Fill in form SA1.”
GOV.UK: Check how to register for Self Assessment · checked 14 October 2026
Free help and HMRC contacts
GOV.UK's Self Assessment general enquiries page says you can ask HMRC's digital assistant for help with registering for Self Assessment, and gives 0300 200 3310 for queries about Self Assessment returns, payments, replacements or notices. The page does not name SA1.
“You can ask our digital assistant for help with: … registering for Self Assessment … Call HMRC if you have a query about: … your Self Assessment returns, payments, replacements or notices … Telephone: 0300 200 3310 … Find out about call charges”
GOV.UK: Self Assessment: general 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.
- GOV.UK: Check how to register for Self Assessment (checked 14 Oct 2026)
- GOV.UK: Self Assessment: general enquiries (checked 14 Oct 2026)
- GOV.UK: Get help from HMRC if you need extra support (checked 7 Oct 2026)
- GOV.UK: Appoint someone to deal with HMRC on your behalf (checked 7 Oct 2026)
- TaxAid: About us (checked 8 Oct 2026)
- Citizens Advice: About us (checked 7 Oct 2026)