Want to know the regulations? - ask the CAA. They are masters in this area. There are pages and pages of rules just waiting to trip up the unwary. Be careful, the CAA will be quick to prosecute if you don't have the right bits of paper.
What a pity they didn't pay so much attention to some other bits of paper - the AAIB reports which recommended the replacement of the clevis lug of the Hughes 300 helicopter. If they had bothered to put pen to paper to implement this recommendation, several people would still be alive today.
Instead, they seem to find it easier to deal with more important issues like prosecuting a well respected pilot for his omission in obtaining a piece of paper that had, by the CAA's own admission, no safety implications whatsoever, and would have been issued had it been asked for.
Seems to me they should take a good long look at their priorities