@lasseb - The same rules apply in the UK. MEP rating lasts for 12 months from date of issue; SEP lasts 24 months from date of issue.
To clarify (or atleast reiterate what has already been mentioned here), the MEP and ME-IR are not related to eachother. They are both seperate ratings, and can be renewed independently of eachother.
The MEP rating can only be renewed in the aircraft, whereas the ME-IR can be renewed every other year in the simulator.
You can let the MEP lapse as you will not need it unless you intend to fly twin prop aircraft; airlines do not care about your MEP, its the ME-IR that they want.
I believe the MEP is required for initial ME-IR issue (i may be wrong), but beyond this you do not need it.
As above, every other year you will also be required to renew the ME-IR in a real twin aircraft. You do not need a valid MEP to do this, nor do you have to renew the MEP at the same time (if you don't need the MEP, don't renew it!).
The reason why people renew MEPs at the same time as the ME-IR in the aircraft is because it is only a small 'add-on'; a few extra circuits and some general flying/nav. It adds an extra 0.5hrs onto your test, so it makes financial sense if you really want the MEP.
@ReleasePT - I would try and clarify the regulations in your case with a local flying school, as I believe your licensing authority are mistaken. Or rather, the person you have been speaking with is mis-informed. As above, the MEP is a completely independent rating, and the validity of your ME-IR is not influenced by the former. Simply put, you can hold an ME-IR indefinately by renewing in both simulators and real aircraft without ever gaining your MEP rating back on your license!
Hope this helps
EDIT : Having written the above, I don't even think the MEP is required for initial ME-IR issue.
Afterall, the MEP is a rating to fly a type of aircraft. The ME-IR is a rating to fly in instrument conditions on an aircraft type on which you are rated. So this really re-emphasises how unconnected the 2 are; You can have the MEP and fly in VFR conditions, or you could hold a ME-IR and not exercise its privileges should you lack the MEP (or any other multi-engined aircraft type rating - ie A320,B737 etc etc)
Last edited by Tsym; 1st Mar 2012 at 12:16.