Flight oops,
If you intend to get your IR within 36 months then do the ATPL exams, as they cover you for the IR. If not, then just do the CPL's, as after a time period (36months?)they expire anyway, so you will have to do the IR writtens again. If you do the ATPL exams, the CAA will only issue with a CPL licence anyway, which will be upraded after you met all the requirements of the ATPL (IR, 350hr multicrew, 1000odd hours TT).
Seems you should save yourself the extra effort now, get the CPL, and sometime down the line study for the IR. In my opinion, unless you get north sea type work, its pointless getting an ATPL anyway, as the only difference between a CPL and an ATPL is that you can fly multicrew.
OD