Clive Hughes' book is called "The Guide to Getting a Commercial Pilot Licence". Mine's a couple of years old (and therefore probably out of date!) but it is a mine of information if you're looking to go the whole way with the ATPL. It hasn't got an ISBN, so Amazon
et al won't be of any use, but you can either get it direct (look in the back of Flyer) or from Transair.
A quick peruse would suggest that an IMC doesn't count towards a multi-IR, but there is (or at least was) a twist. If you go to the States and do the FAA single IR, which costs about the same, it will convert direct to the CAA IMC,
and exempt you from some of the multi-IR. Which will hopefully save some cash.
I'm sure someone will now come along and tell me I've been talking rubbish again.
