Everything to do with nuclear weapons - design, engineering, support, maintenance, retirement, manpower - is frighteningly expensive. When it came with its own pot of money there was a certain attraction in owning it, now it has to be paid from the same money box the costs involved impinge upon all other programmes.
The RAF is en-route since 1991 to shrink from 30 FJ squadrons to 6, with concomitant manpower; the RN has in the same period seen the FFG/DDG fleet shrink from around 50 to 20 and the attack sub fleet from 25 to 7 - now manning and equipping the carriers will put even more strain on the rest of the fleet as the inevitable cost overruns occur.
I think the Trident replacement is becoming a poison chalice the RAF is more than happy for the RN to remain responsible for - and the RN increasingly unhappy.