do you have kids? or can you borrow some? ;D
find out if hackney has surestart in the area. it's a government funded scheme to improve the lives of pre-school children living in 'deprived' areas.
i have found them to be wonderful allies in getting things done, round here they've turned heaps of wasteland into playgrounds, quadrupled council streetcleaning rounds etc etc.
if you can convince them that wasteland should be made available for allotments so that young families can access higher quality food, excercise and so on, especially if many live in flats, then they will get it done. they are mr Blair's darlings at the mo and have huge political clout.