So Kaizen never made it to Grantham, it just wasn't ready in time. The wheels continue to be a problem, I got some M12 plates to mount the wheels to, drilled out the bolt holes to M8 and they are fine but, perhaps a little naively, the threadlock on the motorshaft just isn't enough, it tore a wheel off.

I have a last roll of the dice, I have some different M12 hubs, I'll see about drilling a bolt through the threaded sections of the hubs and the motor shaft to try and lock these in place but I don't think I have the facilities to do that with, certainly not the upper body strength to do so. If I can't get them done, I really don't know what to do next.