BA 767's at Heathrow are mainly used on a variety of European routes; Madrid, Barcelona, Moscow etc.
At Gatwick, they are used for long-hauls (Caracas&Bogota) and are just about to start flying to Nassau and Providenciales (Turks&Caicos Islands). Another 767 route I can think of is Entebbe (for Kampala, Uganda).
Trintocan, I was at LHR on the 26th too, in the morning. I was flying in a Classic 747 from BOS. We were parked next to G-ZZZA a BA777 in old c/s.
(My trip report is in the other forum).