The only restictions applying are use in Class A airways, use outside the UK and 'recommended' approach minima.
1800m?
[/Pedant mode off]
It does seem a bit bizarre though. Pilots with IMC ratings are happily and safely operating through the UK on an almost daily basis. They are not bumping into other aircraft and there is no evidence (is there?) of increased erosions/level busts or breaches of regulations by IMCr pilots operating under IFR.
So, where is the evidence that an IMCr (or IR-Lite) would be unsafe in all CAS?