Firstly, I must apologise for replying to my own post. I posted my question on this forum a few days ago but without any replies, I emailed 50cycles. I received an automated email saying they were at the Earls Court Cycle Show so no answer there for a few days. With next weeks commuting getting closer I decided to get the spanners out. It seems that the gear cable replacement is quite straightforward but involves some dismantling of the bike. Briefly, here's how I did it. Detailed help if required.
The gear cable can be removed from the rear hub by lifting the cable end assembly from the cassette joint pulley after putting the twist grip to position 1
Shimano Nexus 7-speed and 8-speed Internal Gear Hubs-Technical data.
The grey plastic casing around the chain and bottom bracket and has to be removed by undoing a bolt and a couple of screws and removing three plastic mouldings out of the way. The motor and pedal assembly then has to be dropped out of the frame by removing 3 allen bolts. The pedal/motor assembly is still attached to the bike by various electrical wires so to avoid putting strain on the wiring I tied mine up to the frame. The other end of the gear cable can be accessed by removing a single screw on the twist grip, removing a plastic cover and withdrawing the inner cable. The rubber grommet where the cable enters the frame has to be pulled free and then the whole outer cable can be pulled out of the frame. Replacement is a reversal of the above process. The new cable can be fed down through the frame and accessed where bottom bracket would normally be.
