Just to clarify what Bookworm said:
To revalidate a SEP class rating you must either:
Fly 12 hours in the last 12 months of which 6 hrs must be PIC and must include 12 take-offs and landings
and
Fly one hour dual with an FI or CRI which can be replaced by any proficiency test or check (the IMC rating counts) and which counts towards the 12 hours.
OR
In the 3 months prior to expiry fly a Licensing Proficiency Check (LPC) with a Class Rating Examiner (CRE)
Look at JAR-FCL 1.245(b):
http://www.jaa.nl/jar/jar/355000/355312/355312.pdf