There was a programme last night ("Inside Out") on BBC South looking at motorists who don't pass cyclists wide enough (recommendation is 1.5m!). That then went on to a spokesman (for a road safety group? I can't remember the name) who brought up that very subject of presumed fault. He said it was still being looked at, and the latest suggestion was that in an accident, the "most powerful" object was deemed to be at fault unless proven otherwise. So In a car/cyclist or car/pedestrian accident the car would be at fault, whereas in a cyclist/pedestrian accident the cyclist would be at fault. Well, I guess you might be lucky and get a car number plate if the car drove off, but how do you ID a cyclist who drives off?
Never mind dash or helmet cams, it won't be long before we're all wearing personal cams! :-)