Many have advised against it. I have an IMC and really, I cannot see why, specifically, doing the IR first is a bad idea.
Well it's entirely up to you, but as you asked for the advice, I would say that there is a HUGE gulf between the IMC rating and the IR. The CPL course will improve your overall flying, your awareness, airmanship, captaincy etc. etc. You will be MUCH better prepared to tackle the IR course after completing the CPL.
On the flip side, better find out you're not upto it before coughing up for the CPL?
That makes no sense at all - why cough up £12 - £15,000 for a multi IR to see if you are up to the CPL (which costs about £5000)???
M