There is an excellent FAQ for this sort of thing at
http://www.higherplane.flyer.co.uk/faq.htm - in particular
http://www.higherplane.flyer.co.uk/faq.htm##9 addresses license revalidation.
My understanding, and I do stand to be corrected here, is that the current requirements to revalidate a PPL(A) SEP rating are as follows:
Option 1: 12 hours logged in the 12 months preceeding renewal, including at least 6 hours P1 and at least a 1 hour flight with an instructor (not, for example, two 30 minutes flights). The
instructor you fly with must sign your logbook and an
examiner must sign your Certificate of Experience/Revalidation included in your license. That's right -
TWO signatures are required, and if either if not done before the 2 years are up, then you have to use Option 2...
Option 2: a line proficiency check (mini-GFT) with an examiner, appropriately signed off by the examiner in both license and logbook.
It seems that the examiner's signature required in "option 1" is often not widely known about and a number of licenses are therefore invalid even though the flying requirements have been satisfied. The examiner's signature
cannot be backdated - miss the date on your CofE/CofR even by one day and you have to take the mini-GFT option. It is perhaps a shame that a clear document giving the rules in full is not available on the CAA website (or if it is then it's somewhere I can't find it!) The topic was covered in some depth at the CAA Safety Evening held at Shoreham a few months ago.
I know the Ops teams at a number of flying schools have been warned to watch out for violations of the "two signatures or you're out" rule. They will (quite rightly) refuse to release aircraft to PPLs with lapsed paperwork as the insurance will be invalid, but this obviously won't catch those people who fly their own aeroplanes.
Fly safe - and with two signatures.
MD.