Record keeping primarily lies in the hands of the individual holding cryptoassets. While crypto exchanges provide some form of transaction records, these records last only a limited time and could no longer be existing come the time for tax return filing.
Hence, you, as the prudent crypto holder, should keep a record of the following, encompassing all cryptoassets you have:
Number of units
Transaction values in pound sterling
State of the tokens (bought or sold)
The cumulative total of all crypto investment units held