To add some reference to Base leg's answer :
JAR-FCL 1.185 (June 1, 2000)
(a) An IR(A) is valid for one year. If a ME IR(A) is to be revalidated, the holder shall complete the instrument requirements of JAR-FCL 1.245(b)(1), which may be conducted in a flight simulator or FNPT II.
(b) If the IR(A) is valid for use in single-pilot operations, the revalidation shall be completed in EITHER multi-pilot operations or single-pilot operations.
If the IR(A) is restricted for use in multi-pilot operations only, the revalidation shall be completed in multi-pilot operations.
[...]
(e) If the IR(A) has not been revalidated/renewed within the preceding 7 years, the holder will be required to retake the IR(A) theoretical knowledge examination.
Some flight schools around offer very good deals for the MEIR renewal, so staying current is not out of reach (in addition to being advisable) !
MF