Ok gentlemen (and ladies). I have at last found time from my chauffeuring duties.
Voltages across the three wires. measured singly , haven't got enough clip on test leads at the mo.
Lathe at rest
A-B 438 volts
A-C 450 volts
C-B 437 volts
Motor on low speed, no chuck turning,
A-B 433
A-C 430
C-B 414
Motor on low speed, chuck turning at fastest possible in low speed, 380 rpm (max mechanical load)
A-B 428
A-C 415
C-B 413
Motor attempted start in high speed, but motor never starts.
A-B drop to 370
A-C drop to 320
C-B drop to 360
Looks to my uneducated eye that ? wire B is the weakling (? generated circuit) and perhaps I should swap B and C ?. ( see Jeroen's post above.).