HMRC sees cryptocurrencies, not as a currency, but as investment assets and so transactions are subject to Capital Gains Tax.
You might need to pay Capital Gains Tax when you:
Your gain is normally the difference between what you paid for the cryptoasset and what you sold it for. If the cryptoasset was free, you will need to use the market value when working out your gain.
Income tax, instead of Capital Gains Tax, would only apply to dealers that are generating trading profits in cryptoassets. It would be very rare for HMRC to assess an individual’s cryptoassets activity to be applicable to Income Tax and this is likely to only affect professional traders and businesses.