It has to be a JAA class-rating examiner with approval to conduct IR renewals - local flying schools should be able to put you in contact with someone. It is technically a 'proficiency check' but there is a specific set of exercises to be done (nearly all of those you did for your initial test!) and if you don't meet the required standard then the examiner will not revalidate your rating so make sure you're ready before you take the test.
Just a couple of points on renewing in the sim:
- the sim has to be approved for IR revalidations (easy - check this with the school / examiner);
- MEP class rating and IR(MEP) are separate ratings and you can only renew the IR bit in the sim; if you want to renew your MEP rating (or both the MEP and the IR in the same flight), this MUST be done in an aircraft.
Hope this makes it clearer!