The great news was I was able to play for about an hour ... not that it was one hours playing - but about 40 minutes I suppose.
In actual fact my the time the pain was starting in my hand I was also getting a sore mouth - not having touched my clarinet for 11 weeks my mouth has gone tender as well!!
Still, I was pleased how well my finger worked - and I only fell over one set of notes, so it looks as if that is yet another box ticked!!