Having been to the Wee-kend and listened to the perceived wisdom, it looks like the most likely reason for loss of drive is a loose nut on the end of the tapered gearbox output shaft. It came to light after we'd come back to find Barry and as I was trying to bumpstart the bike because the magnets had fallen off inside the Valeo starter motor earlier in the trip


Just as well it happened trying to bumpstart it rather than when relying on engine braking coming down a mountain.
Top marks so far for CN in getting me back, and repatriating the bike hopefully within 2 weeks