Just an update on this - bike went back to dealer today, and with the help of Technical they have diagnosed a faulty clutch switch. Being replaced in about a weeks time.
(As a courtesy bike they gave me a C600 scooter - it was rubbish! My tmax is loads better)
So I had the clutch switch replaced last week, since when I haven't had the problem. I haven't done loads of miles since, but I was previously getting the fault about once every time I rode the bike, so ... so far, so good!


Thank goodness this is now a factory option