405 estate rear suspension collapsed

[firemoth]

Hi. As above, on way back home with caravan on the m6, massive bang and back left of car dipped down a lot. No noises or anything so it's on the stops. Still on hard shoulder so not had chance to look properly but it definitely is collapsed suspension. I'm assuming it's new back axle. What can I take out from? I've got a saloon sat at home as my spares bin, will that be the same or will it have to be from an estate? If so, what am I looking at cost wise? Is it a DIY job? I've done a normal rear axle on a mk6 escort before, but nothing with torsion bars.

Any advise greatly appreciated. Thanks