I would like to draw your attention to a prime site for guerrilla gardening.
It is alongside the Greenway at hackney Wick within view of the Olympic stadium. They have just installed a new water main and there is a large area of freshly tilled soil just waiting to be seeded and planted. No clearing or digging required.
I'll be putting the primroses & daffs from my window boxes in when they have finished flowering, but the area is so large it could do with a blitz from the guerrilla gardeners.
See link below.
http://wikimapia.org/#lat=51.53714&lon=-0.022949&z=18&l=0&m=s&v=2