I was gonna say that based on my experience with 50's and 60's Triumphsm Beezers and Nortons, the BA stands for Bass Ackwards. But we've got good British folk on the forum and I don't want to irritate anybody. Boy, I sure miss the old Lucas electrics.
BWolf, best sockets you can buy (not brand but type) are 6 point metric. They can accomodate other than name plate sizes without rounding and work with American sizes as well. I don't think there's anything on your Bullet that's Whitworth. It seems to be all metric.