The government shortlisted 15 proposals for new settlements in April and has said up to 10 final approved bids will have to go through the planning process once they have been chosen later this year.

Green space

They would comprise of between 5,000 and 20,000 homes each.

Lawyers John Steel QC and James Strachan, representing the Local Government Association (LGA), said an existing planning policy statement included rules on providing housing in new settlements in an environmentally sustainable way.

This meant Thursday's statement - which is expected to lay out guidelines such as eco-town homes having to be within 10 minutes of frequent public transport and leaving 40% of space as green undeveloped land - was unnecessary.

It could also be illegal, as it would lead to the government bypassing planning procedures run by councils, the lawyers added.

There did not seem to be any justification for promoting eco-towns outside the existing rules, "other than the government's wish to avoid the system due to the proper need for scrutiny, which takes time", they added.

The LGA said the legal advice showed the government's approach to eco-towns was "deeply flawed".

But Ms Flint told BBC Radio 4's The World at One: "Myself and government lawyers completely disagree with the LGA's claims.

"I think that they possibly presented to their lawyers a misrepresentation of their point to come up with the press release they have [put out] today."

Ms Flint said planning applications for eco-towns would have to "go through the full process".

Bidders for eco-towns at Manby, in Lincolnshire, and Curborough, Staffordshire, have pulled out, while part of a third bid at New Marston, in Bedfordshire, has also been withdrawn.

'Stretching standards'

A Department for Communities and Local Government spokesman said: "We absolutely disagree with the LGA's claims and believe this legal advice can only have been obtained on the basis of a misrepresentation of our policy.

"We have made it absolutely clear throughout that eco-towns will be different and will have higher environmental standards than a normal development and the applications will also have to be considered through the normal planning process."

Shadow housing minister Grant Shapps said the legal advice would add weight to the argument that ministers had "effectively destroyed their own eco-town project".

Liberal Democrat communities spokeswoman Julia Goldsworthy said: "What this government fails to understand is that centrally imposed solutions are doomed to failure."