JRF have what looks to be some interesting research on delivering affordable homes. They conclude:
S106 for affordable housing has proved to be robust in the face of continuing uncertainties. However, tensions are building up within the system regarding other planning obligations; the types of dwellings delivered; the use of grants; and the fact that many local authority plans are out-of-date. There are further tensions arising from uncertainties about broader policies, notably the impact of Government approaches to capturing planning gain, on what can be achieved in terms of affordable housing. Finally there are fundamental concerns about the realism of some LPA [Local Planning Authorities] housing policies as rising affordable housing targets increasingly lead to viability issues, an issue that is unlikely to be resolved by clearer government guidance.
I had an interesting chat about this sort of thing with the Deputy Mayor yesterday, but don’t know how much of it was on the record, so I won’t say anything more than things seem to be afoot.