Airbridge
Was there not something done to the airbridge stand that B A uses for LHR that restricts it to A320 and below. I think it happened when the 757 stopped being used on the route some time ago. However when it was re introduced they had to be parked elsewhere and passengers had to walk quite a distance to/from the aircraft. Cant remember the detail.
Its about time capacity on the LHR was increased but are you sure its an 321, The BA schedules show a 320 on all services next summer wheras a few weeks ago it was showing all 319s???.