The Campaign to Protect Rural England (CPRE) is concerned at the plans for a "growth corridor" out from London.

The organisation says the new homes will present a "grave threat to the countryside".

The East of England Regional Assembly (EERA) has backed the scheme and says it aims to improve the quality of life for people in the region.

On Monday, Henry Oliver, CPRE head of planning, criticised the plans which call for new homes between now and 2021.

'Deeply damaging'

He said the plans, which would affect land between London and Peterborough, "pose a grave threat to the countryside and towns of Cambridgeshire, Essex and Hertfordshire".

"The Regional Assembly members know this plan is deeply damaging.

"Their own independent sustainability report on it warned that further development on any significant scale would be `intrinsically damaging' to the region's environment.

"Yet they have insisted on pressing ahead with plans for growth on a huge scale, regardless of the cost to the environment and quality of life of everyone in the region.

"The tragedy is that this plan could fail to achieve either of those, but still eat up our valued countryside."

The CPRE said the proposals could include irreversible damage to landscapes, wildlife, rural tranquillity, water resources, air quality, recreation and the character of historic cities, villages and towns.

Homes for key workers

Traffic would increase, worsening already bad congestion and contributing to climate change, the CPRE fears.

Deputy Prime Minister John Prescott is backing the expansion plans.

He argued that key workers such as teachers, nurses and firefighters needed low-cost affordable homes but were being pushed out of the market by London's soaring property prices.