To keep your IR current, you will need to do either short test (easier than initial) or have completed certain criteria. (no. of sectors and approaches)...each year.
You do not have ot do this each year if you are skint or have no job. However if you leave this longer than 5 (or is it 7) years, you will need to meet a CAAFU examiner again!
Similar applies to class ratings. 2 years for SEP 1 year for MEP. Either have thge experience to be signed off or short revalidation test!
Please feel free to correct if i have got some bits wrong.