Less than 5 years since the date of expiry of your last C of E ('13 month stamp' as was):
Exams: NONE
Training: Sufficient to prepare for a Proficiency Check with a UK/FE(PPL).
Test: SEP Revalidation Proficiency check with a UK/FE(PPL).
Cost: To CAA - NOTHING!! To Examiner - whatever he/she charges. Otherwise whatever your Club charges for ac hire.
Paperwork: Examiner will sign off your LPC SPA form (you then send it to the CAA) and will also sign your FCL150CJAR - the form which now goes into your licence to replace the old '13 month stamp'. You can then fly with passengers.
Validity: 24 months from the date of the Proficiency Check. In the second year you must fly either 12 hours, of which 6 must be as P1 and must include 12 take-offs and landings PLUS a 1 hr training flight with a FI, OR just fly another LPC SPA (with an Examiner) in the last 3 months of the validity period.