Ive just got in from replacing the discs on the front of my ST170 Focus and have sheared the locking nut key off. But . . . its sitting on non standard wheels which have wheel specific nuts which is where the problem lies!

Its fitted with 17 BSA Bullet wheels but the nuts are internal drive rather than the usual external drive type fitted to most other wheels, I have about 5mm exposed from the wheels so have to use that to try to remove the nut. Does anyone have any useful suggestions to help me get this bloody nut off without wrecking anything?

Cheers,
Paul