More greenfield sites look set be earmarked for housing under controversial plans to be outlined next week by the deputy prime minister, John Prescott.

Under the proposal, expected in a consultation paper, planning authorities would be forced to release more land for housing in areas where house prices are high.

The idea was put forward last year by the economist Kate Barker in her review of housing supply for the Treasury.

She said extra land should be released for new homes in areas where house prices rise above agreed thresholds. The idea has alarmed planners and countryside campaigners, but the government is believed to support it as a way of achieving a "step change" in the number of new homes built in the south-east of England.

Speaking at a Town and Country Planning Association conference this Wednesday, Mr Prescott said: "Too often in the past, the planning system has failed to respond to changing demand for homes in different places. We want plans to take better account of housing markets and need and reflect the needs and circumstances of different areas."