Billions of pounds must be found for land regeneration if government plans for affordable new homes are to be met, house builders have warned.

On Friday, the House Builders Federation (HBF) welcomed government plans to target Milton Keynes, the Stansted-Cambridge corridor, Ashford in Kent and the Thames Gateway for development.

But Pierre Williams, spokesman for the HBF, said that questions remained over where the money - to clean up run down industrial brownfield sites and make them fit for homes - would come from.

On Wednesday, Deputy Prime Minister John Prescott announced the development plans which will be backed with £22bn over three years.

Prescott's plans: 2003-2031

London-Cambridge-M11 corridor: Between 250,000 and 500,000 new homes Milton Keynes: Up to 300,000 new homes Thames Gateway: Up to 40,000 new homes Ashford: Up to 31,000 new homes

Mr Williams said: "Many will now be asking questions as to how the promised investment of £22bn nationwide will be spent.

"The sum appears considerable but has to be compared to the colossal costs of tackling decades of under-investment in housing.

"Even if the money is spent effectively, it will not solve the problem."

The government wants more homes built on formerly derelict sites near city centres and good transport links, which should reduce private car use.

Martin Leyland, strategic land director for Wilson Connolly, one of the UK's leading house-builders, called for better communication between developers and ministers and criticised slow planning regulations for holding up development.

The government says more homes are needed

He said: "It would be a mistake to root the debate over housing in theory and ignore the practical side to the issue.

"House-builders have a good bank of land, brownfield and greenfield, suitable to meet the government's identified needs for development.

"The problem is getting the planning process moving.

"Making bold statements about new houses in a few key towns is one thing, but there are plenty of log-jammed projects sitting in the pipeline.

"We encourage the government not to focus only on the headline-grabbing fast track proposals at towns such as Milton Keynes, but also concentrate on delivering much needed homes in other locations."