It was a bit of a mission, but I managed to change tubes and tyres without totally removing the motored wheel. Undo the wheel-nuts and slip them both in past the nut on whichever side is easiest. Then you can feed it onto the rim.However it looks like in future if I have to get a new tube then it's up to Halfords for them to remove the rear wheel for the job to be done.
Take pics before you start. Then you'll know what goes where, when you reassemble it.