Stuffy
It wasn't me; it was the other boy.
The RAF's A330s cannot be fitted with an ARB - its a PFI. It wasn't in the requirement (because at the time the only aircraft we had in the inventory that required boom refuelling was the E3D and that can also do probe and drogue) and it would cost an absolute fortune to add it now!! C-17
was a lease and AAR was prohibited under the lease terms, so no requirement. Regretably the bean counters will not allow expenditure on something for which we have no "requirement" - even if it makes military sense in the interoperability department.
As to P8 v Nimrod
MR1/MR2, well Duncs has answered that one (very different if you are talking MRA4 - but they also are, as Duncs says, bean tins); but you still haven't explained why you think 4 - 5 hours of transit time
and 4 hours on task isn't good enough for an MPA?