All automatic gates at the exit area from the northern line are exits.
For the entrance/exit area to the Northern Line, the left-hand gates are generally the ones you need, though the direction of individual gates may vary according to the time of day.
For the Jubilee Line, the right-hand gates are generally the ones you need.
At the time of our survey, we found no pattern as to the direction of these gates. There is, however, a manual gate at each end of this gate line.
LONDON BRIDGE UNDERGROUND STATION
© 2008, Terry Robinson