WCollins is correct - the IMC rating can be renewed by most club CFIs (they changed their name recently, but we know what we mean) - most CFIs are also examiners. The IR is altogether a different fish, with a renewal check flight every year. Prohibitive for most of us.
IMC - relatively easy to get; needs regular practice to keep it current. Provides a good compromise for UK-based PPLs who want to fly IFR in IMC, but who don't want to (or can't) do the full IR.
Trouble is, despite occasional bar talk to the contrary, the IMC rating is not recognised outside the UK.
If the IMC works for you, then after 50 hours or so of "use", you can do an FAA IR for relatively little expense. If you can get your hands on an N-reg aircraft, then you can fly IFR in IMC all over.