It's taken a while but I think I have sorted out the problem.
The air inlet pipe to the air cleaner has a rubber end, (both ends, but it was the open end causing the problem) the rubber had folded into the inlet pipe thus restricting the airflow, so far none of the high revs at idle (the revs still hang under accelaration but have been told by loads of people this is normal for the engine in this model)
