The gates at TXL 'A' are arranged in a hexagon alignment, and the roadway does not have access to the areas away from the central 'drop-off' point.
http://www.berlin-airport.de/EN/Reis...adEnglisch.pdf
The distance is not too great, and can be easily walked.
IIRC (and it's been a decade for me flying AF out of TXL), BA uses either A3 or A4, and AF uses either A14 or A15 (corrections are welcome).