This mattress was beside a footbridge over the A40 Western Avenue in an area that was known as Leadville because of all the pollution. Here is the introduction to "Leadville: A Biography of the A40" by Edward Platt (Picador).
"Whenever I was driven into London, I watched the houses which lined the road: as the car travelled towards the centre of the city, the houses marched in the opposite direction; dirty and anonymous, pinched and choked by an endless, ragged chain of cars and lorries, they looked uninhabitable, yet the blackened cars parked on their pavements suggested otherwise. It seemed incredible that there were people living within ten yards of the car in which I was travelling.
One afternoon in January 1995, as I drove along Western Avenue, I did what I had never done before: I parked the car in a side-street, and walked on to the road..."