Small commercial vessels operating under the UK flag and in UK waters must comply with the Merchant Shipping Regulations or an MCA Code of Practice.
While not a requirement for pleasure craft, this publication may be of interest.
Guidence for Masters and Watch Keepers
From: Maritime and Coastguard Agency
Safety codes of practice for small (up to 24m) vessels
Contains public sector information licensed under the Open Government Licence v3.0
