Have you looked in Lasors on the Caa's website?
It gives a pretty detailed explanation of what hurdles to jump and can be downloaded here:
LASORS: LASORS 2010 | Publications | CAA
Look at section G5.3 - Expired licenses.
If you are within 5 years of one of the Type or Classes in you're license being valid it should be quite straight forward. Greater than 5 years means re-sitting written's and flight tests.