There is a capital loss of £100,000 in the 22/23 tax year, upon un-staking the 10 BTC. The disposal proceeds are £200,000, but the acquisition cost upon entry was £300,000. This capital loss of £100,000 in 22/23 cannot be carried back to reduce the £200,000 capital gain realised on entry in 21/22. Therefore the £40,000 CGT remains payable by 31 January 2023, even though the value of the BTC has dropped significantly in value. The £100,000 loss can only be set against capital gains in 22/23 and future years.