Conservative MPs are calling on the government to insist that at least two-thirds of new homes are built on so-called 'brown-field' sites - urban areas which need cleaning up.

Liberal Democrats want to raise that figure to three-quarters, and press Deputy Prime Minister John Prescott to block any projects outside towns until the government has set out its policy.

John Prescott has backed building new homes on green belt land

Mr Prescott has been under fire since he revealed that the UK needed at least 4.4 million new homes between now and 2016 to cope with demographic changes.

He supported the idea of building two million houses in the countryside to avoid overcrowding in cities and towns.

But Mr Prescott, who as Secretary of State for Environment has overall responsibility for house building, has since backed away from the controversial policy.

He now proposes that at least half the new homes should be built on brown-field sites.

But with critics saying that is still not good enough, both the Tories and Liberal Democrats are likely to cross swords with Labour in the Commons and demand tighter controls on green belt building.

The looming homes crisis has come as experts predict that demand for housing will be far greater in the next century than previously thought.

An initial projection of 4.4 million new households from 1991 to 2016 is now thought to be one million too low.

Experts say that while the population will remain stable, the number of people living alone will increase, putting pressure on existing housing.

The Joseph Rowntree Foundation says that the government needs to double annual funding for low-cost homes planned by local councils and housing associations.