Immediately before the RN assumed the deterrent role, the V-Force had about 9 Vulcan and two Victor sqns with 11 ac on QRA. The SSBN brought 16 weapons to the party and the V Force reduced to about 7 or 8 sqns, ie follow on force of 50 or so weapons.
The Vanguard class can probably field a similar number of MIRV on its own.
The number of target sets will not have changed significantly.
For an aircraft based system you would need to accept a reversion to a similar Leningrad/Moscow system and need 11-12 QRA as defences would have improved in step as well. A further 40 aircraft would be needed to match the Vanguard follow on numbers