Well, so MMB would have me believe.

In the printable version of the itinerary, I get this...

"Check-in
ba.com online check-in opens 24 hours before departure and closes 1 hour before departure. We recommend you check in online for this flight and print your own boarding pass. If you have baggage to check in, please go to any of the Bag Drop desks in Zones B, C, D, F or G (at the airport)
Self service kiosk check-in opens 4:45am on day of departure and closes 45 minutes before departure. Please check-in and print your Boarding Pass at one of the 80 check-in kiosks located in Zones B, C, D, F, or G at the airport.
Airport desk check-in opens 3 hours before departure for Bag Drop and closes 45 minutes before departure for Bag Drop. Once you have checked in and printed your own boarding pass, please take your bags to a Bag Drop desk located in zones B, C, D, F or G. Bag Drop desks open daily from 5:00am

After Check In
Galleries Club T5A & T5B
Location: Galleries Club Lounges are located in both the North and South areas of Terminal 5A, and in the main Gate area of T5B. Please follow signs for North Lounge, South Lounge or the T5B Gates after going through Security.
Galleries Lounges offer an environment that allows you to catch up on work before you travel, enjoy a snack or simply unwind in an area that is relaxing and away from the busy airport environment. (Please refer to terms & conditions in membership benefits)"

Hmm...One can only try!