Originally Posted by Ozzy
My original plan was to go to T1 domestic BA lounge (going through immigration line) then when ready go back through and transfer to T2.
I haven't got anything to add to the advice already given.
However, if you do find yourself wanting and able to use a T1 BA departure lounge, use the international one. The reason is that you can get from that lounge to the T2 gates without having to pass through the Flight Connections Centre or undergoing any further security screen. The airside areas of T1 international and T2 are directly joined by an elevated corridor, which makes this very easy. From the T1 international BA lounge, first follow the signs towards gates 50-something which take you along the side of the Flight Connections Centre smoking area (unmissable, but fortunately on the other side of a glass wall). You should then start seeing signs for Terminal 2 departures - just follow them around the far end of the FCC and then into that corridor.