There's an awful lot of emotive guff talked about carriers.
1) The UK can now longer afford to carry out the full spectrum of military roles and operations, and has to concentrate on those core 'defence of the UK' capabilities that cannot be left to allies, and those that we need every time we go on ops. We cannot retain every niche capability - no matter how well we may have undertaken them in the past.
Britain won't be standing alone, re-fighting the Battle of the Atlantic as the RN bravely defends the convoys against the Hun, nor even against Ivan, since it's been decided that we won't conduct that scale of op alone and autonomously.
2) The UK's aircraft carriers have not been NEEDED since 1982 (they've been used, and they've been useful, but not needed in a "only carriers could do this" way). Even a repeat of the Falklands would not REQUIRE the use of carriers today.
3) In EVERY incident in which UK carriers have been used, land-based air power could have got there quicker, cheaper, and with greater capability once in theatre. (Nor am I overlooking Sierra Leone, when a Jaguar squadron was available on the Azores, with the necessary permissions to operate from Dakar, long before Grey Funnel lines got there.....)
4) While you can never GUARANTEE HNS, I would suggest that if such support is unavailable, the proposed op is probably unsustainable anyway. But if such an op is sustainable, and is stopped only by our lack of carriers, then we have plenty of allies who do have carriers.
5) Aircraft carriers are by no means 'self contained' - they require AD frigates, an SSN, tankers, RFAs, etc. - a small Armada. And they can sustain a relatively modest sortie rate for a relatively short period of time.
6) By canning the carriers now, and JSF, all of the other capability areas that are now being slowly strangled by funding constraints could be afforded - including tankers, SH, SEAD, etc.