Lou,
If (as you state) you have any current UK or JAR-FCL licence, even with a lapsed medical, all you will need to do is:
1. Obtain a (minimum of) a JAA Class 2 medical certificate.
2. Fly whatever you and your FIs think you need to prepare you for a Single Engine Piston (Class) Rating Renewal Skill Test.
3. Fly the test with a UK/FE(PPL) or higher.
The test consists of:
Pre-flight prep.
Take-off, climb to height.
Steep turns
A couple of stalls, one of which must be a clean, fully-developed stall and standard stall recovery with minimum loss of height.
Off-aerodrome PFL
Normal and flapless circuits, including an EFATO and a go-around.
Rejected take-off (e.g. engine failure on last touch-and-go)
Takes just under an hour.
If your Rating has lapsed by more than 5 years, you'll be asked oral questions by the Examiner.
NO WRITTEN EXAMS!!