Notso Fantastic,
I renewed my SEP rating as a way to renew my UK ATPL a year or so ago. I currently fly a B777, but on a foreign licence and do not have the T7 on my UK licence.
I keep my UK Class 1 Medical current but almost 6 years had passed since I has an LPC on my last UK type (B757) rating, and had therefore expired. The 2 things that are required to renew an ATPL are 1) a current medical and 2) a current type (or class) rating.
I popped my to the UK, went and had a chat with a flying club and found that as it was less than 5 years since my SEP rating had expired, all that was required was 'sufficient' training and a Skills Test (LPC). I recall that I did about 2.5 hours refresher and a 1.5 hour test which consisted of upper air work, some navigation, and a few circuits. Had the SEP rating lapsed for more than 5 years, then the CAA has to issue the rating, rather than the examiner. LASORS will explain everything you need to know, Section F.
Hope that helps.