The part-FCL PPL is a lifetime licence, so does not itself have any revalidation criteria as such.
The revalidation requirements for SEP Class Ratings are described in FCL.740A sub-pararaph (b) on .pdf page 40/200:
(b) Revalidation of single-pilot single-engine class ratings.
(1) Single-engine piston aeroplane class ratings and TMG ratings. For revalidation of single-pilot single-engine piston aeroplane class ratings or TMG class ratings the applicant shall:
(i) within the 3 months preceding the expiry date of the rating, pass a proficiency check in the relevant class in accordance with Appendix 9 to this Part with an examiner; or
(ii) within the 12 months preceding the expiry date of the rating, complete 12 hours of flight time in the relevant class, including:
— 6 hours as PIC,
— 12 take-offs and 12 landings, and
— a training flight of at least 1 hour with a flight instructor (FI) or a class rating instructor (CRI). Applicants shall be exempted from this flight if they have passed a class or type rating proficiency check or skill test in any other class or type of aeroplane.
(2) When applicants hold both a single-engine piston aeroplane-land class rating and a TMG rating, they may complete the requirements of (1) in either class, and achieve revalidation of both ratings.
Out of interest, did anyone else find it impossible to download a copy of the .pdf to which David referred? The only way I was able to save a copy was to 'print' the whole thing using CutePDF Writer to create a .pdf replica.