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, would swallow up vast tracts of green field sites in the district.

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. 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.

Yesterday, the council's executive member for the environment, Ilkley 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.