Solved this problem:-
I noticed that if I killed task `kicker` cpu usuge returned to normal, but I lost taskbar (and kasbar).
So after systematically removing taskbar applets and panels I noticed the problem was linked to kasbar (removing kasbar fixed problem).
I`ve grown to love kasbar, so loaded it back up, and looked at the settings, narrowed it down to working ok with `enable progress indicator` disabled.
I can live with that