Well this is strange. 2 days before going in, system started working perfectly again. No faults found, no messages, no codes.
Dealer has gone back to factory for advice, so continuing asis until we get a response. Car needs a service in c. 2000 miles anyway, so hopefully it will hang ok until then. I can then get a loaner whilst they do more investigation and service it.
Might have my rear footrests in by then too