Broken Shimano Nexus 8 Gear Hub
it has never had an oil dunk - but it is just about to get one.
I have found out the cause of the broken hub!
I decided to dismantle the hub and found the cause almost immediately - it is a completely shattered ball bearing cage on the non-drive side of the hub. Cost of a new one - less than a fiver. Great relief.
So relieved in fact I have decided to service the hub myself and have sent for the special Shimano hub grease and "dunking" kit - at a cost of over £80!
It looks pretty straight forward (hopefully not famous last words).