Guy from our local Triumph dealership picked up the bike today and got the prognosis this afternoon.
Apparently one of the cogs (sorry i can't be more specific) - the smaller one to the far left of the clutch. Had become dislodged to the point that it was totally out of alignment.
Ray - i think that might be the starter drive you were referring to?
Anyway they took it apart and put it back together again and apart from some slight wearing of the starter motor it starts first time.
The cost? a hours labour and a case of beers (so about 60 something quid plus beers).
Good guys over there, heart attack over.
Ant