The way I see it is you pulled out into on coming traffic. You are supposed to give way when pulling out. 100% Your Fault.;)
I would disagree with this as an outright statement for several reasons.
(1) In a shopping car park, it is reasonable to drive in forwards (thus reversing out) because the boot needs to be accessible for loading goods.
(2) There is frequently a difficulty in seeing any traffic passing your rear, because adjacent vehicles, particularly commercial ones, will cause significant obstruction of your view.
(3) The only solution is to reverse
very slowly, looking for better vision as early as possible, and being ready to stop, having knowledge of the chances that a vehicle may cut across your rear.
(4) A driver passing the rear of vehicles so parked is (or should be) quite aware of the situation, and therefore approach with equal care, at a slow speed, and be prepared for the need to stop.
(5) Failure to observe these actions, particularly if driving against clearly displayed arrows, is a contributory act of carelessness.
(6) Contrary to what some drivers may think, in a public carpark, any act of carelessness which results in injury to persons or property can still be subject to police bringing charges.
(Example: On such a carpark, my wife and daughter witnessed a car hitting another parked one, and then being driven off. They gave details to the owner, and the police prosecuted the offending driver).
I would agree that it is an argument which could go either way. The best course is to get a witness(es) if possible. If you have witnesses who firmly believe the driver was acting carelessly, also ensure that the police are informed.
In public carparks, the requirement for care applies to
all drivers; not just those reversing out of a parking place. It is a situation where every case has to be judged on its merits.
I was once following another car in a shopping precinct carpark; both of us looking for a space. The car in front suddenly stopped just past a vacant place, and I pulled up a couple of yards or so behind him. He then immediately reversed towards this space, and in his rush for the spot collided with my car.
Could have been difficult, me being to his rear, but I had a witness, and he collected 100% of the blame.