If you want to do aeros in a Yak, go to Gennady Elfimov at Skytrace
http://www.skytrace.co.uk (Halfpenny Green or what should now be called Wolverhampton Business Airport). You could also try Jez Hopkinson at Compton Abbas
http://www.aerobatics.co.uk although I'm not sure he's still doing the AOPA course. Heard Dawnpatrol are also pretty good in the Extra 300L.