Even if the A330 did burn the extra fuel you assert (which it most certainly does not), because the 767 has so much less capability, to match the A330 the RAF would need to use many more old Boeings than they would new 330s. Remember, as even Buff Hoon just announced, it's not the number of platforms which matters, it's what you can do with them. And the RAF will be able to do far more with the A330 than ever it would with ba's cast-off 767s.