Well I seem to have found a way to avoid the knee jump I was getting. I set the limits in the shins to to stop them twisting or swinging, also set limits in the feet to prevent swing, then turned limits on for the figure.

This set up gives me a few glitches in the feet, but these should be easier to correct than the knee jump. It was Cage mentioning joint twisting as a possible cause that put me onthe right track. Thanks Cage.