So in the back of my ex-police Vectra, between the two rear suspension turrets (very close to the rear seats) there is a bar, it's like a steel box section bar, about 3/4 inch thick. Seems to be connected to the suspension turrets but TBH haven't had a proper look yet.
It does have two holes in about a third in on either side.
Perhaps dual-purpose, strut brace and something solid to bolt some sort of kit onto.
I haven't had any chance to chuck the car about a bit, what with the bad weather and needing new ARB bushes. So I don't know how well it handles yet.