for the answers to the most common questions, the CAA usually direct people to their General Information Documents (GID's). these can be foound on the Safety Regulation Group's web site if you know where to look!
In relation to the requirements for renewal / revalidation of a civilian PPL(A) GID 33 refers.
The URL for this particular GID is:
<a href="http://www.srg.caa.co.uk/documents/srg_fcl_gid33.pdf" target="_blank">http://www.srg.caa.co.uk/documents/srg_fcl_gid33.pdf</a>
Hope this helps.