(I know this is an older thread, but I figured I'd provide some more recent/updated info for those who may want it.)

The BA Galleries lounge is located in Terminal 1, Module B. After you clear immigration and security at 1B, take a left and head to the end of the terminal. You'll follow a dingy hallway and go up an old elevator (or take the stairs on the side). Just follow the signs to the BA Lounge down the small hallway. (The Delta lounge is no longer there.)

The BA Galleries lounge probably seats 50 or so. The furnishings are nice and don't feel old; don't let the depressing 1970s hallway outside fool you. There are 6-8 computer workstations set-up. Wifi is available; just ask the front-desk for the code. Basic Galleries food set-up: espresso/cappuccino machine with biscuits, finger sandwiches, small hot food buffet (3-4 items). Also standard bar set-up: beers, soft drinks, and tonic in the fridges; wine and spirits on the counter.

WC is outside of the club. Take a left as you go out the doors; they're right next to the elevator.