Hi Grzegorz Brzęczyk,
Yes, you would need to obtain the market value in pounds sterling, of the cryptocurrency at the time you are gifted it and the diposal value in pounds sterling at the time you dispose of it.
If the difference, minus costs is a positive number, you have a gain.
If you have unused annual exempt allowance to set against the gain, this will reduce the amount taxable.
You would report and pay your gain tax liability using the onine realtime transaction service here:
Report and pay your Capital Gains Tax
Or on a Self Assessment tax return if after 31 December after the tax year has ended.
Thank you.