Beam has cracked/separated on the front edge of cylinder that holds the bush.
Was on a speed bump actually, not fast or big, just rolled over it and heard a big thunk and then the scraping of the rear wheel on the arch.
I think I was very lucky it happened in a retail park not on the motorway.
Cheers for that, I had wondered if VW had routed the brakes through it, the technical drawings don't help in that respect. and I'll have to double check but I'm 99% sure my bogo spec rules out abs, I've certainly not seen it pop up on the dashboard.