The Commons environmental audit committee's report says councils are expected to demonstrate five years' supply of housing available now on brownfield sites, whereas developers can call on virtually limitless supplies of green belt land.
It urged the government to reintroduce a clear sequential test in favour of brownfield development and suspend implementation of its regional spatial strategies until it has published an environmental appraisal of its house building targets.
"With the economic decline, developers will cherry-pick green belt land over less profitable brownfield sites," said Campaign to Protect Rural England (CPRE) senior planner Kate Gordon.
"It is vital that, in the current market downturn, targets are revised to ensure that we recycle brownfield land and bring empty buildings back into use before developing on green fields."
But a DCLG spokesman responded: "What the CPRE fails to say is that since 1997, overall green belt land has grown by 33,000ha. The overwhelming majority of homes, 77 per cent last year, are being built on brownfield land. Building on brownfield remains our clear priority."
Greener Homes for the Future? An Environmental Analysis of the Government's House Building Plans is available at PlanningResource.co.uk/doc