These cars aren't tail happy at all. To get mine to lose the back end I'd have to really try and unsettle the rear, lift off and turn in violently. If I'm pushing it out of a roundabout it just grips, and the first thing to go would be the front. But that's never happened as I'd have to be driving like a loon to even get it to understeer.
I'm on 30mm H&R springs, MPSS all round, full Hunter geo in the last year.
Something aint right with your car mate.