Originally Posted by
flatlander
Then walk diagonally across almost the entire airport towards the gates D21-D31 which is where BA leave from (always that end of the airport, sometimes nearer you). If you have time and lounge access, you can go upstairs near the end of the D pier to the BA lounge, but it's got basic drink and minimal food provision with a nice view.
Do NOT automattically go to to the end of the D pier if you are on the 10:15 LHR flight, as the OP is. The BA429 is the scheduled B763 which cannot go on the D24-D28 normal BA gates and will go on D4 usually.