There is no credit towards a JAR IR if you have an IMC rating.
However, there is one roundabout way of getting an hours reduction. It is possible to get credit towards an FAA IR. This is because the requirements for an FAA IR are for xxx amount of hours instrument flying, of which yyy (a much lower number) must be with an FAA CFII. Your IMC rating, and any time you've spent flying around the UK using this rating, all count towards xxx, leaving you with just yyy hours to do. You can then do a 15-hour conversion to a JAR IR. I can't remember the exact hours-requirements for the FAA rating, but I seem to recall that the total hours required (assuming you already have an IMC rating) will be less than doing a JAR IR to start with.
FFF
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