British HMRC warns of triple the number of untaxed crypto gains cases

British tax authority HM Revenue & Customs (HMRC) has given me a real jolt this week: the number of warnings about potentially undeclared crypto gains has almost tripled in just one year. In the first half of 2025 alone, the agency has already sent over 1,200 targeted notices to taxpayers who may have failed to report – or fully report – profits from crypto transactions. It is clear how seriously the British government is taking this issue and how much harder it is becoming for investors to avoid detection by the taxman.
A warning sign: why HMRC is now cracking down so hard
According to a recent HMRC report, the number of such warnings has jumped 280 percent compared to last year – from 450 notices in the whole of 2024 to over 1,200 in just six months of 2025. This is no accident; it is the result of deliberate action. The agency uses advanced data analytics tools to identify suspicious activity, not just high-value gains but also frequent transactions or unusual patterns that may indicate undeclared income.
Investors who trade crypto assets on foreign platforms or use multiple wallets to obscure profits are particularly in the spotlight. HMRC makes it clear: this is not about isolated incidents but systematic checks. “We are pursuing this with full rigour,” states a spokeswoman for the authority.
What crypto investors need to know
In the UK, gains from cryptocurrencies such as Bitcoin or Ethereum are taxable – whether you sell them, swap them for other assets, or even use them as payment. HMRC distinguishes between two main categories:
1. Capital Gains Tax (CGT): Applies when you dispose of crypto at a profit. The annual tax-free allowance is £3,000 (2025 rate).
2. Income Tax: Applies to rewards from mining, staking, or receiving crypto as salary or payment



. Tax is charged at standard income tax rates.
Many investors remain unsure about when and how to declare such gains. HMRC is stepping up efforts to clarify the rules through awareness campaigns and direct warnings. “We want to help people avoid mistakes before they become costly,” says an HMRC official.
What happens if you do not declare your crypto gains?
Failing to report crypto profits can lead not only to back taxes with interest but also significant penalties. HMRC can impose fines of up to 100 percent of the undeclared amount, and even more in repeat cases. The challenge is compounded by the fact that many foreign exchanges do not automatically share customer data with UK authorities. Therefore, HMRC relies on international cooperation – for example through the OECD – and has set up special task forces dedicated solely to tackling crypto-related tax evasion.
A tax expert sums it up bluntly: “The days when you could quietly pocket crypto gains without paying tax are over.”
The future: a global crackdown on undeclared crypto gains
What Britain is doing is part of a worldwide trend. Countries such as the United States, Germany and the Netherlands are tightening their own controls. HMRC plans to expand its data analytics capabilities and pursue cases with even greater precision.
For investors, the message is clear: now is the time to get fully acquainted with your tax obligations. Experts advise meticulous record-keeping of every transaction and seeking professional help early if in doubt. “Acting now can save you from heavy back taxes and penalties,” warns a chartered accountant.
HMRC has made it plain: it will intensify its efforts over the coming months. Those who do not act now may soon face the consequences. The era of complacency is definitely over.