HM Revenue & Customs sent 81,172 letters, emails and text messages to cryptocurrency holders during the 2025-26 financial year, sharply expanding its campaign targeting potential unpaid tax on digital asset gains, the BBC reported.

The 81,172 compliance warnings were nearly three times the 27,714 issued in 2023-24. The communications are designed to prompt recipients to review their tax affairs, rather than to serve as evidence that every person contacted has underpaid tax. For crypto users, that distinction matters because HMRC has increasingly broad access to the records needed to check whether gains, swaps or other disposals were reported correctly.

The escalation comes as HMRC gains access to a much larger pool of customer and transaction data from crypto platforms operating in the UK.

Crypto Swaps Can Trigger Capital Gains Tax

UK tax obligations extend beyond selling Bitcoin or another asset for pounds. Exchanging one cryptoasset for another, spending crypto, or giving it away can each qualify as a disposal for Capital Gains Tax purposes.

HMRC maintains a dedicated cryptoasset disclosure service for taxpayers who identify previously undeclared income or gains involving exchange tokens, NFTs and utility tokens.

The agency's expanding compliance campaign follows the UK's decision to require crypto firms to collect transaction and customer data under the Cryptoasset Reporting Framework (CARF). For active traders, records can therefore extend across centralized exchanges, token swaps, wallet transactions and other disposals, rather than only fiat withdrawals. That broader reporting picture is central to why the compliance drive is widening now: HMRC is pairing warning letters with a data pipeline that is designed to make undeclared activity easier to identify.

CARF Gives HMRC a Larger Data Pipeline

The UK's CARF regime took effect on January 1, 2026, requiring reporting cryptoasset service providers to collect identifying information and tax-relevant transaction data from users. HMRC's official reporting rules require providers to submit summaries covering reportable users and their transactions, with the first reports due to be filed between January 1 and May 31, 2027.

International information exchange will widen that visibility further as participating jurisdictions begin sharing crypto transaction data. The rollout has already raised privacy concerns as CARF and other tax-reporting frameworks expand globally. HMRC's own guidance states that data received under CARF will be used to identify and risk-assess taxpayers and support compliance work. In practical terms, the first wave of reports will help HMRC connect account holders, transactions and tax returns across platforms, while the warning letters give recipients a chance to review their records before that reporting flow fully matures.

Reporting Rules Target £315M in Additional Revenue

The government expects the reporting framework to generate £315 million in additional tax revenue through 2029-30. HMRC's official CARF impact assessment projects £40 million in additional revenue for 2026-27, followed by £110 million in 2027-28, £85 million in 2028-29 and £80 million in 2029-30.

The warnings were sent before HMRC receives the first complete set of transaction reports under the new framework, with UK crypto providers due to submit their first CARF reports by May 31, 2027. That means the current outreach phase is happening ahead of the first full reporting cycle, as the tax authority lays the groundwork for a system in which crypto activity is increasingly documented through standardized disclosures rather than self-reporting alone.