Colapsed Wall

[kimbo9]

My parents have a lane leading to thier house, the lane is owned by them and there is an old stone wall that runs down one side with a 40 foot drop the other side. At the bottom is a council run car park. Over the weekend this wall has colapsed taking part of thier lane with it, so much so that now the car is now suck outside the house as there is no longer enough lane width to drive it down. Who is responsible? The wall is on the right as you go towards the house, but on the left when you look from the house.