From the hallowed pages of the SRG website, I find (undated, of course) the following...
" Ratings/Endorsements - SEP: How do I renew an expired SEP rating?
For a period not exceeding 5 years from the expiry date of your SEP rating, you will be required to pass a Licensing Proficiency Check. To renew an SEP rating that has expired by more than 5 years you must pass the SPA Skill Test on a SE Piston (Land) aeroplane at an FTO (Flight Training Organisation) or a Registered Facility."
Now...this guy has never had an SEP rating -he has only had a UK National Group A PPL.
It seems to suggest that the LPC is for checks of less than five years overdue, that the full skill test (nav and all) is for checks over five years and it also seems to suggest that there are NO minimum requirements other than "pass the test".