Oliver Scott

Hi, I'm a British national and I've bought some cryptocurrency. I want to send this to a friend's wallet abroad. I'm aware I need to pay CGT on any gains I've had on it at the point of sending. How do I record the info on current prices at point of sending - just note down prices according to a typical crypto coin exchange (they might slightly differ) on a spreadsheet? Is there anything else I should keep a record of for HMRC purposes? Or anything I need to do before or afterwards? Most of these things would be able to be checked in retrospect I'm sure but just wanting to know how to do this properly. Many thanks