In all truth the larger capacity Trident 3s were most suited for the densest but quite short routes from Heathrow, to Paris (when not Tristar operated), Amsterdam, and the UK Shuttle trunks. These didn't need a lot of fuel and didn't get a lot of freight, so were quite lightweight. There were sufficient 2Es for the longer runs.
The shortfall in 3B capacity while the wing mods were being done led to BOA- um, er, BA Long Haul Division loaning a couple of spare VC-10s to BE - um, er, BA European Division, to cover things, to an extent that they appear formally scheduled in a 1979 timetable I have, to Amsterdam, Lisbon, etc.
Blind pew, if you were flying the Shuttle routes at the end of their Trident operation in the early 1980s, I quite likely was pax behind you. Did you make that stunning departure I had from Manchester for Heathrow one afternoon when I was seated in the final rearward-facing seat row, looking at my new, prospective, serious client in the first forward-facing row opposite, who were it not for my seatbelt would have got me slam in his face when we rotated on liftoff. "Gripper" my a**e !