The number of houses planned for green belt land has nearly doubled over the past year, according to new figures.
Some 150,000 homes and 1,000 hectares of mines and commercial premises are being proposed for the areas, research by the Campaign to Protect Rural England found.
Previous analysis suggested just 81,000 homes were planned in August 2012.
The group said the figures raised serious concerns about whether ministers were keeping their promises to safeguard the green belt.
Spokesman Paul Miner said: "The extent to which the threat is growing - nearly doubling in a year - is deeply worrying.
"It should not be necessary to build on green belt land when there is enough brownfield land available for a million and a half new homes.
"Green belts prevent urban sprawl and are the green lungs of many of our largest or most historic towns and cities.
"Ministers now need to go further. Hard decisions are needed to help ensure both urban regeneration and protection of the green belt'."