You must have missed the bowser Chevvron, The Volga-Dnepr Group quotes range at max payload as 4,500km. Wiki gives it a maximum range (payload not noted) of 5,200km.
Doesn't work I'm afraid.
This was in the days before TAG. Farnborough Business Aviation (FBA) operated the FBO from a small enclave south side with DERA/MOD operating north side.
FBA had a single 5000l bowser and limited underground tankage, about 12,000l I think, just sufficient to service their normal bizjets. This wouldn't be sufficient to supply 3 aircraft like AN124s.
DERA wouldn't have been able to help; they were only keeping minimum amount of AVTUR for their own needs as they were about to move to Boscombe Down.
Even a couple of years later when FBA had got a bigger bowser and DERA flying had gone, they were asked to re-fuel a visting C5 Galaxy (transporting POTUS helicopters) and after emptying their bowser twice said that was all they could do.