The Environmental Audit Committee, a cross-party group of MPs which scrutinizes policy, have said that housing targets should be reassessed.

They say the 3m target was not justified after the credit-crunch, with changes in the mortgage market and falling house prices.

It warned pressure to provide land for so many homes - which may not be needed now the housing market has slowed - could lead to greenfield sites being developed unnecessarily.

Greener Homes for the Future? An environmental analysis of the Government's house-building plans, said measures favouring brownfield sites over greenfield land should be reintroduced, and planning policy strengthened to protect existing greenbelt boundaries.

The report also recommends that:

* Targets to make all homes zero-carbon by 2016 should be used to speed up development of locally-situated community renewable energy sources

*With the economic slowdown, ministers should increase the proportion of the planned new houses that are built after 2016 - when regulations come in which demand all new homes are "zero-carbon".

The government has to make a formal response to the recommendations.