UK cryptocurrency investors may still owe taxes even if they have not received warning letters from HMRC, as the agency intensifies its efforts to track unreported digital asset income. In the 2024-25 tax year, HMRC sent nearly 65,000 reminder letters, doubling the previous year's total. Tax experts highlight that increased data sharing and international agreements mean non-responders are not exempt from obligations. Andrew Duka of Awaken Tax warns that failing to report crypto transactions is illegal, urging proactive compliance. HMRC identifies non-compliance by cross-referencing bank records, exchange data, and self-assessment forms, with high-income investors and those with large on-chain assets more likely to be targeted. Exchanges in the UK or serving UK clients must provide transaction data to HMRC, and the OECD's crypto asset reporting framework will further enhance data collection from 2026. Investors are advised to voluntarily report taxable events such as token swaps, staking, airdrops, and yield farming to avoid penalties.