Greengage is following closely new research which suggests that more than half of English councils with greenbelt land are preparing to allocate some of it for development ahead of brownfield sites.
The findings come as new national planning practice guidance is due to be issued by the government early in 2014.
CPRE 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. However more than half of the 147 local authorities that responded to the National Trust survey said they had brownfield sites that could help meet the five-year housing land supply target.
Government statistics published in November also seemed to endorse the concern, revealing that green belt land in England had decreased by 130 hectares in the 12 months to March 2012. However, this accounts for less than 0.01 per cent of the total area designated as green belt, which makes up around 13 per cent of the country.