Private developers put up cash for roads and schools

The research, which was commissioned by the Department of Communities and Local Government, shows planning obligations have led to the "very substantial" investments by developers.

Planning obligations known as S106 agreements are negotiated by council planning authorities when granting permission for new developments.

These ensure that the necessary infrastructure to support new developments is in place and also that developers create "mixed" communities by providing some affordable housing on new private estates.

The researchers, from a joint team at Sheffield and Cambridge universities, found that nearly two thirds of new affordable homes were now provided through S106 agreements.

Until recently, little was known about the extent and value of these planning obligations. Professor Tony Crook, who led the research team, said: "The last decade of this century has seen a very substantial increase in these contributions by developers, facilitated by the significant increase in land values.

"The size of the country's future requirement for new homes will require a substantial investment in infrastructure to support it, whilst the Government's target for new homes includes increased targets for affordable homes."

Dr Gemma Burgess, one of the co-authors of the study, added: "This report illustrates the increasingly important role S106 agreements have played over the last few years in contributing to local infrastructure and supporting affordable housing."