the ford ka has been running fine recently until tonight, i reversed back 2 feet literally, heard a really loud bang, thought i had hit something, got out the car and the ka had totally collapsed at the back, is this a common problem with the ka? what is it likely to be? its lower at the offside back than the nearside but still very very low. the ka is a 03 base model with only 15000 miles on the clock.

any info much appreciated

thanks

Sounds like the spring may have broken (it's happened twice to me (not in KAs) but at the front. I blame speedbumps.
If that's what has happened, you'll need to replace both sides at the back, as the other one may not be far off collapsing either.
It's not an expensive thing to have done. Cost me around £300 both times (Volvo 240 and Renault Laguna estate) so my be cheaper on the Ka.