Your licence is valid for 5 years. It's your SEP class rating that would need to be revalidated. This is valid for 2 years, but as you passed last summer, you still have a year and a half to run on it. To revalidate the SEP rating, there are several routes - the easiest is to do 12 hours in your second year ( including an hour with an instructor who'll sign you off ). So technically you don't actually need to do anything at all. The club you're with will probably insist on a checkride though.
Incidentally, you're in exactly the same position as me. I passed in September, did a few hours over the autumn, and stopped over the winter. I'm looking to restart and have several sessions booked next week - and it looks like rain. Thanks UK weather
