Very briefly(ish):
You'll need 1 whole hour with an instructor to revalidate by experience if you go the '12 hours in the final year' route.
If you run out of time, you'll need to do a Licence Proficiency Test with an examiner (I believe that's the correct term) to revalidate a PPL. That's essentially a GST: EFATO, stalls, steep turns, PFL, normal, flapless and glide approaches etc, possibly with a bit of nav thrown in.
Whilst the first option needs to be signed off by an examiner before the licence expiry date, the second option will revalidate your licence even if it has expired, ie there's no rush.
There is a further option - keep your PPL, comply with the revalidation requirements for an NPPL and fly with an NPPL Medical Declaration from your GP until your PPL expires. NPPL restrictions will apply (no night, no IMC, no flight abroad etc) so it depends upon the type of flying you do. Before your 'PPL' expires you apply for an NPPL and carry on flying with that.
The advantage is that the Medical Declaration (which cost me £25) lasts 5 years and the revalidation requirements are less onerous (see nppl.co.uk for details). Snag is that some examiners are a bit twitchy with this route as they have been left in a bit of an administrative no-mans land due to poor implementation of the special arrangements.
I considered the NPPL/PPL route but eventually decided to revalidate my PPL by experience because it was so much simpler and quicker - luckily I have sufficient time.
I'm sure there will be a renewals guru along in a minute to give you chapter and verse, but at least that's an outline of the options to be going on with!