HMRC Has Sent 100,000 Warning Letters to Crypto Investors — What You Need to Do

HMRC has sent over 100,000 capital gains tax warning letters to crypto investors since 2020. The pace is accelerating — 8,329 in 2021/22, 27,712 in 2023/24, and 64,982 in 2024/25 alone. That's a 680% increase in three years.

If you've bought, sold, swapped, staked, or provided liquidity with crypto, you are on HMRC's radar. And from January 2026, your exchange is telling them exactly what you've been doing.

This guide explains what's happening, what it means for you, and what you need to do before the next self-assessment deadline.

What are the warning letters?

HMRC calls them "one to many" nudge letters. They're sent to taxpayers whose records suggest they've sold, exchanged, or received crypto without fully declaring the gains or income on their tax return.

The letters aren't accusatory — HMRC frames them as "encouraging voluntary compliance." But make no mistake: if you receive one, HMRC already has data suggesting a discrepancy between what you declared and what your exchange reported.

Crypto investors have received 40 times more CGT warning letters than stock traders since 2020. HMRC is clearly treating crypto as a priority enforcement area.

Why now? CARF changes everything

The real shift happened on 1 January 2026, when the Crypto-Asset Reporting Framework (CARF) came into force in the UK. This is an OECD-designed framework that requires crypto platforms to report user transaction data directly to tax authorities.

Around 50 UK crypto service providers — exchanges, custodial wallet providers, and some DeFi platforms with controlling entities — are now collecting and reporting:

• Your name, address, date of birth, and tax residency
• Your National Insurance number or tax reference
• Full transaction records: purchase price, sale price, profits
• Every disposal, sale, swap, and transfer
• Annual transaction summaries

The first reports are due to HMRC by 31 May 2027, covering the 2026 calendar year. But HMRC already has historical data from exchanges collected under existing Finance Act powers — CARF just makes the reporting automatic, comprehensive, and standardised.

What HMRC can see now vs before

The Treasury estimates CARF will raise £315 million in unpaid tax by 2030. That money has to come from somewhere — and it's coming from the returns HMRC can now cross-check against exchange-reported data.

What counts as a taxable event

Many investors assume they only owe tax when they "cash out" to GBP. That's wrong. HMRC treats all of the following as disposals that trigger Capital Gains Tax:

• Selling crypto for GBP or any fiat currency
• Swapping one crypto for another (including ETH → USDC)
• Paying for goods or services with crypto
• Adding liquidity to a DeFi pool (disposal of deposited tokens)
• Staking where you receive a different token (e.g. ETH → stETH)

Note on bridging: Cross-chain bridges (e.g. ETH from Ethereum to Arbitrum) are a grey area. HMRC has not explicitly ruled on bridges. The conservative view is that bridging transfers your cost basis across chains without triggering a disposal, since you hold the same asset on a different network. Some advisers take the opposite position. If you have significant bridging activity, get professional advice.

Additionally, staking rewards, airdrops, and mining income are taxable as miscellaneous income at the market value when you receive them, taxed at your income tax rate (20–45%).

The penalties for getting it wrong

HMRC's penalty regime is tiered based on the severity of the error:

On top of penalties, HMRC charges daily interest on outstanding balances, plus late payment surcharges of 5% at 30 days, 6 months, and 12 months.

The investigation lookback periods are also tiered: 4 years for innocent errors, 6 years for careless errors, and up to 20 years for deliberate non-disclosure. With CARF data flowing from 2027, HMRC will have the evidence to pursue cases going back years.

What you need to do

1. Check if you have undeclared disposals. Every crypto-to-crypto swap, LP deposit, and staking event is a disposal. If you only declared when you cashed out to GBP, your return is incomplete.
2. Gather your transaction history. Export data from every exchange and wallet you've used. For DeFi activity, you'll need on-chain data from block explorers — exchange CSVs won't capture it.
3. Calculate your gains correctly. HMRC requires Section 104 pooling with same-day and 30-day bed-and-breakfast matching rules. A simple "bought at X, sold at Y" calculation is not sufficient. See our complete 2024/25 guide →
4. Separate income from capital gains. Staking rewards, airdrops, and LP fees are income (taxed at 20–45%). The underlying token disposals are CGT (taxed at 18–24%). These go on different parts of your self-assessment. Read our staking tax guide →
5. Amend past returns if needed. You can amend a return within 12 months of the filing deadline. Beyond that, you can make a voluntary disclosure to HMRC. The sooner you do it, the lower the penalties.
6. Don't ignore the letter. If you've received a nudge letter, you have 60 days to respond. Ignoring it doesn't make it go away — it escalates it.

The bigger picture

The UK is part of an initial group of 48 countries implementing CARF simultaneously. From 2027, these countries will automatically share crypto transaction data with each other. Using an overseas exchange doesn't help — if it operates in a CARF jurisdiction, the data is shared with HMRC anyway.

The era of crypto being a grey area for tax is over. HMRC now has the infrastructure to match exchange data against self-assessment returns at scale. The 100,000 warning letters were sent with incomplete data — imagine what happens when the automated CARF feeds start flowing.

The good news: if you get your records in order now, you're ahead of the curve. Most crypto investors haven't. That's why HMRC expects to collect £315 million in unpaid tax by 2030.