HMRC letter codes · One-to-many letters
CAMM3MMLetter about tax on cryptoasset transactions
Published by its source on 23 July 2026. A date in the letter that has passed stays passed: what a passed date means.
Last reviewed 14 October 2026 · How Tax Letters checks its facts
In short
HMRC's letter CAMM3MM says HMRC wants to help the reader understand when they need to report cryptoasset transactions and how to update their tax position.
“CAMM3MM … We want to help you understand when you need to report cryptoasset transactions, and how to update your tax position.”
ICAEW: HMRC letter CAMM3MM, as published with its tax news item · checked 14 October 2026
Information, not advice: this page reports what HMRC, GOV.UK and the bodies named publish about CAMM3MM. Each fact has its source and the day it was checked beside it.
When HMRC sends it
ICAEW publishes HMRC's letter CAMM3MM beside its news item, which says that between July 2026 and March 2027 HMRC’s Wealthy and Mid-sized Business Compliance team will contact individuals it believes may have underpaid income tax or capital gains tax (CGT) arising on transactions in cryptoassets.
“Between July 2026 and March 2027, HMRC’s Wealthy and Mid-sized Business Compliance team will contact individuals it believes may have underpaid income tax or capital gains tax (CGT) arising on transactions in cryptoassets.”
ICAEW: HMRC targets tax liabilities from cryptoassets · checked 14 October 2026
What it asks
ICAEW's news item on HMRC's letter CAMM3MM says a taxpayer with income or gains to report should amend their self assessment tax return for the tax year in question or, if too late to amend, use HMRC's disclosure service.
“Where the taxpayer has income or gains to report, they should: … amend their self assessment tax return … for the tax year in question; or … where they are too late to amend their return, … use HMRC's disclosure service”
ICAEW: HMRC targets tax liabilities from cryptoassets · checked 14 October 2026
Free help and HMRC contacts
HMRC's letter CAMM3MM gives the phone number 03000 552294 for questions about making an amendment or a disclosure.
“If you have questions about how to make an amendment or a disclosure, or you want to give us information about your cryptoasset transactions, you can: … call us on 03000 552294”
ICAEW: HMRC letter CAMM3MM, as published with its tax news item · checked 14 October 2026
ICAEW's news item on HMRC's letter CAMM3MM lists the GOV.UK pages “Check if you need to pay tax when you sell cryptoassets” and “Check if you need to pay tax when you receive cryptoassets”.
“Check if you need to pay tax when you sell cryptoassets - GOV.UK … Check if you need to pay tax when you receive cryptoassets - GOV.UK”
ICAEW: HMRC targets tax liabilities from cryptoassets · 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.
- ICAEW: HMRC letter CAMM3MM, as published with its tax news item (checked 14 Oct 2026)
- ICAEW: HMRC targets tax liabilities from cryptoassets (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)