Bradford needs the equivalent of a new town to meet its future housing needs, a controversial study has calculated.

But campaigners warned today that the building of more than 30,000 new homes, as suggested in a draft regional planning blueprint, will swallow up vast tracts of green field sites.

The bombshell figure by the Yorkshire and Humber Assembly is based on the district's population, which is expected to grow faster than anywhere else in West Yorkshire.

But it is more than twice the number of new homes calculated to be needed in the next decade by Bradford Council planners who drew up the latest Unitary Development Plan.

The assembly predicts Bradford's population will rise from 477,000 in 2003 to 559,000 in 2023.

Its estimate of demand for homes also takes into account an anticipated boost in the economy for areas around Leeds.

It therefore estimates the district will need 1,950 new homes a year up to 2016, then climbing to 2,370 a year up to 2021.

But the Council is planning a full-scale challenge to the yet-to-be published draft regional spatial strategy document which will go to the Office of the Deputy Prime Minister in December for consideration. That will be followed by a major public consultation exercise expected to end with a hearing equivalent to a public inquiry.

Today, the Council's executive member for the environment, Councillor Anne Hawkesworth, said the authority had already objected to the regional estimates and she warned the district's green fields would be under threat because there were not enough former industrial sites where the homes could be built.

"It would have an overwhelming effect on planning applications," Coun Hawkesworth said.

"We have objected and want them to analyse again the necessity to build this number of homes in the Bradford district. We think the figure is wrong."

Council planning officer Andrew Marshall said it was a "significant increase" and officers were now looking at the district's capacity.

But Andrew Haigh, policy manager of the assembly's regional planning and transport team stressed the figure was provisional.

"It is a start base and we are still discussing the figures. They are based on the Office of National statistic population projections and other factors. The draft is not drawn up. There will be consultation," he said.

Protesters believe the regional plan will be a body blow for thousands of people who fought to save the district's green belt at a £1 million public inquiry into the UDP three years ago.

They could end up with a hollow victory despite the findings of the six-month long inquiry into land use across the district for the next decade as the assembly's planning blueprint will supersede it.

Then campaigners faced formidable challenges from major developers who said the Council had not allocated enough land for new homes in the UDP.

Yet many of the campaigners won their battles and the Council succeeded in delaying development for a number of years on highly controversial sites.

The Council has adopted the UDP, following the public inquiry and accepted the finding that 1,390 houses a year will be needed over the next ten years.

The leader of the Council's Labour group, Councillor Ian Greenwood, said: "We have to recognise there is increasing demand and reach a situation where we can provide more houses.

"It is extremely important we do not get into urban sprawl and we should choose very carefully. The alternative is to tell people they can't live in Bradford and that is unacceptable."

Liberal Democrat group leader, Councillor Jeanette Sunderland, said Bradford planners and Tory councillors had got the figures wrong when future need was estimated in the UDP. She claimed inquiry inspectors had drawn up the green belt "looking at a fag packet".

Richard Lang, a member of the action group which won its battle to stop housing on Jenny Lane playing fields in Baildon, said: "We are enormously concerned that all the work we have done could be overturned.

"We would keep an eye on what happens and act as necessary. It would be an absolute crisis for Baildon."

Councillor Martin Love, leader of the Council's Green group, said the figure produced by regional planners was an over-estimate and the high number of empty homes in the district should have been taken into account.

But Alex Hunter, of the House Builders' Federation, said: "We would welcome figures representative of need."