A confession of failure: a shot of a woman painting graffiti onto the pavement in front of a pre-fab looks to me like it was filmed on the Excalibur Estate in Catford, but I have not found an exact match to the building we see. This looks very similar, but the windows aren't right and there aren't any houses behind like those we can see in the image above:
Ector Road, S.E.6 - Google Street View
You can find out more about the Excalibur Estate on Jim Blackender's blog, here. (Jim tells me he would be 99% confident that the location in the film is the Excalibur Estate.) You can see his wonderful collection of photographs of the Estate here. Below are some samples:
