Pontius N. That is a good point about SSKs and hitting the "supply train". Hit the essential AOR, AO or, by then, MARS and operational endurance immediately becomes limited. That means that the support ships will need to stay inside the Screen. They will still be vulnerable to air attack and underwater attack. To counter the former, there is an intention of 6 T45 DDs. For the latter, by then, we will have no more than 13 T23 FFs (the Future Surface Combatant isn't discussed very much, is it). Assuming no further "savings", that's 19 ships of which not much more than 13 could be expected to be in Fleet Time. Say, 4 DDs for AD and 4 FFs for ASW (on the thin side), that's over half the operational fleet tied to one operation.
A very simplistic back-of-a-fag-packet assessment; but it does suggest that DD/FF force will be below that needed for our core Maritime commitments. The danger in the CVFs is that further sacrifices in DD/FF numbers may be needed in order to fund them. The alternatives, without additional and much needed increase in the Defence Budget, are to reduce the core tasks at significant risk or rely on NATO (lets not think about EU!) cover for our capability gaps. The other assumption, of course, is that any Carrier operations undertaken would be part of a US Group and sit under (and over) their umbrella.
Although the CVFs are central to current Maritime (and Joint) Doctrine, as per BR1806, one has to wonder at what overall National risk; unless there is a real increase in the Defence Budget.