I am not aware of any requirement but it would be good practice to do so - no big deal to write down a few details - suggest quantity + name + address + cert no and if really worried have them sign as receiving it.

A member of my ML club drove to the Vesuvit importer (Market Harborough??) and purchased 32 x 1kg tubs of VLC. They assured him that he could transport up to 50 kg in his car with no special arrangements (!). He did have to disburse it all the same day because he could not legally store it, so we all met up in Bisley that evening. He was recording certs but AFAIK he has never been asked to account for that 32kg. As a side note it would have ben even cheaper to purchase it in 16kg bags but none of us fancied dividing it up.

I doubt that you would be in danger of selling by way of trade if it's just some mates.