New 'eco-towns' will have 15mph speed limit in government bid to make them carbon neutral

The new restriction is among a number of proposals designed to minimise the environmental impact of 10 proposed settlements.

Developers have submitted more than 50 bids to create the zero-carbon developments, and later this week housing minister Caroline Flint will set out standards expected of them.

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The new town centres are to be car-free, and the 15mph limit will be enforced on "key roads" leading into them, government sources said.

No definite date has been set for the announcement of the shortlist of 10 new towns, but it is expected in the coming weeks.

Miss Flint said: "These developments will be exemplars for the rest of the world, not just the rest of the country.

"It's critical that we get it right - and I make no apology for setting the bar as high as possible.

"We have a unique opportunity to deliver a programme which will genuinely revolutionise the way people live."

Ministers also plan to reduce car use drastically in the new towns by providing extensive public transport.

Developers are expected to be told that each home in the eco-towns must be within 400 metres of a public transport stop and 800 metres of shops.

Last month Miss Flint said she wanted to see towns designed around pedestrians, cyclists and public transport users, emulating the "most ambitious European models" where only 50 per cent of households have a car.

Environmental protesters have criticised the eco-towns scheme for focusing too narrowly on carbon emissions and not giving adequate consideration to other ecological issues, such as the impact building would have on wildlife.

Up to five eco-towns are expected to be built by 2016, and as many as 10 by 2020.

They will have populations of around 5,000 to 20,000 and be linked to larger towns and cities.

The proposals have also sparked protests nationwide from residents who claim the schemes will put too much pressure on local services.

Opposition has been voiced in places such as Grovewood in south Derbyshire and Stoughton in Leicestershire, and last month around 300 campaigners marched against plans for a 6,000-home development in Long Marston, near Stratford, Warwickshire.

Nigel Humphries, of the Association of British Drivers, criticised the plans as "bullying" motorists.

"It's one more step towards bringing back a 4mph speed limit and a man with a red flag walking in front of cars," he said.

"They are missing a real opportunity to make the towns pedestrian and cyclist-friendly by keeping them separate from traffic."

The new eco-towns represented an excellent opportunity to build in safe cycle lanes and walkways, he said.

People would only stop using their cars if they had a practical alternative, he said, and public transport was not a viable option for everyone.

"It's all very well for these greenies who are mostly young and fit, but what about the people with families and children?" he asked.

"You can take a baby on the bus, but try doing it and carrying a weekly shop as well."