Where abouts to find old bikes (in general)

rakan Wandsworth council tips is one of the best places in London!

The building i live is in a little alleyway, on one side their are gardens all with falling down fences, i can see someone has a stack of bikes which havent been used for ages piled up in there - however im too scared to either sneak around in their garden or knock on their door because they are always having nasty domestics.

Pics?