I'm not a lawyer, but I do remember the police saying at Bikesafe, that if you overtake past a junction, then the liability is 100% yours as the overtake is unsafe. The driver may never have been able to see you as you would have been coming past the the traffic obscuring his view.
If they are offering a 50/50, in those circumstances, I would probably bite their hand off. I may have misunderstood your description though, in which case if I've got it wrong I apologise in advance!
In this diagram you would have overtaken the purple car, and the driver pulling out wouldn't have seen you...
