Yesterday, I was parked in a car park in front of a row of shops. I think the car beside me must have been reversing out just as I started to reverse, but I don't actually recall if they were arriving into the car park next to me or leaving. The other car was an L plate driver being instructed, not that this probably makes any difference. I looked in the rear view mirror and, of course, proceeded to reverse as there was nothing behind, but I guess I have reversed into their car as the damage is on my passenger rear side colliding into the other cars front drivers side, although it appears I must be at fault because I have seemingly reversed into their car. Is there a clear definition of fault in this car accident? Appreciate any help.