Initial target acquisition of an inbound ASM carrier pre-launch in sufficient time would have been extremely difficult. First the target detection by UKADGE, then the comms link to pass information to the 'Vulcan fighter'. Then the manoeuvring required to achieve the head sector launch of a SA missile... It was difficult enough to achieve the geometry in the Phantom, achieving a 180 x 0 in the much slower Vulcan would have been immensely unlikely unless it just happened to be lucky enough to be in the right place at the right time.
However, decent BNS updates and a self-designating TIALD capability could have made GW1 Euphrates bridge-plinking from 40000ft a distinct possibility - one Vulcan or 3 Tornados, 1 Buccaneer and 2 VC10s?