according to LASORS, yes you will be able to "top up" the exams as JohnGV says. however the CAA's idea of top up is to reduce the minimum classroom hours you need down to about 350 or 200 hours and credit you the IFR/ VFR comms exam if you have got a cpl/IR already. all the other exams will have to be done (all 12 of them). if you only have a cpl and want to get an IR for an ATPL, they will reduce hours and credit you VFR comms only.
in essence, wirlygig ir correct.