JARs, AICs and GIDS do not change the Law. The IMC rating, as already stated, is valid on any Class or Type of aeroplane you are rated to fly.
If you revalidate on a ME aeroplane the test includes asymmetric however, if you revalidate on a SE aeroplane there is nothing in the law (ANO) that prevents you flying a ME aeroplane in IMC. If you do regularly fly a ME aeroplane then common sense says you should consider revalidating on a ME from time to time, after all it can be combined with the mandatory aircraft rating revalidation test.