I've done some further testing and certain that the motor cutout problem is not related to the bearing seizure - not enough and certainly no adverse heat build up in the bearings and I can still freely turn the spindle immediately after it cuts out. The motor cuts out after 3-5 mins running fairly consistently and then takes a few minutes to cool down before it will run again, so I'm guessing there's some thermal cutout on the Brook Crompton, a twitchy breaker on the rear cover or brake or possibly wiring. I guess it could also be a supply fault, but I run the lathe independently from a static 240V single to 415V 3phase converter and no fault indicated here.