Today I turned of the traction control and discovered that, lurking below the surface, the GTi is a Pepperami!
It goes all feral when using a boot of throttle coming out of tight corners or pulling away from junctions (with no "tramping"). And you can feel the diff working more often .... Lovely!
However I might have left some black marks all over Buckinghamshire and there is the tyre wear to consider ....