For the boat, you'll need your ships papers, basically like the registration
certificate for a car and a copy of your insurance
For yourself, if you intend to go outside of UK waters, then you'll need an ICC
(International Certificate of Compitance, bit like a basic driving licence) and you'll also need to have a VHF radio
opperator's certificate (not essential in Europe
but mandatory in UK waters).
If you don't have the last 2 already, then a local RYA school
will be able to sort them out for you.