We currently have 38 HM Mk1. 30 are being converted to HM Mk2, leaving 8 that could be converted to ASaC/AEW. Except that, unlike the Gucci pictures in Flight Global, these airframes are not fitted with a ramp. You can't just fit one, the rear fuselage is completely different. And in this financial climate we're not going to buy any new airframes.
So my guess is that some of the HC Mk3/3a's that we are taking from the RAF would have to used for ASaC/AEW. But this will leave the Junglies short of medium air lift capability and in any case the Mk3/3a cannot be folded i.e. blades and tail pylon are fixed. Not much use at sea if you can't get it in the hangar.