If you believe the UK carriers are vulnerable due to the fact they require oilers every so often then the only answer is a COMPLETELY nuclear powered battle group - including the cruisers, destroyers and frigates that make part of it
Even the USN backed off from that - and all the surface escorts for the CVN's run on oil. So N-power allows the carrier to stay at sea forever but maybe on its own if the oilers are all sunk - is that wise??
I personally think the money should have been spent elsewhere but we'll still have two carriers bigger than anything outside the USA and I'm sure the USN will be happy to see us take over some tasking from their big beasts