Thanks guys.
I can't leave the UK at the moment so have to do all my training locally.
I did consider the issue of icing (no airplanes I am flying are equipped for FIKI), and so am keeping an eye on cloud layer heights and the freezing level on days I am grounded as an example of whether an IMC could actually get me airborne on those days in the kind of aircraft I will be flying.
I will be doing the CBIR most likely, but I am not banking on those 15 hours on an IMC rating being knocked off the IR in their entirety (i.e. not confident that I will be sufficiently proficient to have all 15 hours credited and actually require more than the 30 hours to meet test standard) - partly due to the issue I mentioned in my post above about the possible difference in teaching on the IR and IR(R).