At New York, British Airways have a half share in their own terminal. If you double back up the small escalator (which also leads to the United lounge) there is a reception desk for the BA lounge at the top. First (Golds, and one world Emerald) is on the left, Business (and Silvers) are on the right.
There is a strange sort of pre-lounge lounge on the right as you enter, which is kept dark and supposed to be a kind of quiet area, however as everyone walks past it and its wide open, it is neither quiet nor private and acts really like a kind of overspill section.