Plans to build thousands of new homes in Oxford's Green Belt are being backed by the South East's regional assembly.

Seera has come down firmly in favour of extending Oxford as the most effective way of tackling chronic housing shortages. But it says Bicester and Didcot may have to face extensive new development as well.

The recommendations have left some assembly members threatening a revolt, amid claims that the new planning system was spiralling "out of control," with unelected members rushing ahead with proposals that will change the face of the county.

Seera (South East England Regional Assembly) wants to build 40,000 new homes in central Oxfordshire, with a review of Green Belt boundaries.

The regional planning committee, meeting in Westminster on Monday, will also be asked to back the idea of releasing Green Belt land on the edge of Oxford for housing development. A report to the committee says there should be "a clear steer" towards a level of development in central Oxfordshire significantly higher than previously set by Government. It says house building should rise by a third, from 1,500 homes to 2,000 a year over the next two decades.

The report adds: "While this would involve the release of land from the Green Belt, it would not be of a scale that would undermine the broad extent and function of the Green Belt."

Oxfordshire County Council leader Keith Mitchell, who chairs Seera's regional planning committee, said the recommendations had come as a bomb- shell.

He said: "The Green Belt is now under serious threat. They want to build on it. I chair the committee, but this is not my recommend- ation."

He said he would be seeking cross-party support in a bid to reassert members' control over what will go into the South East Plan, which will decide planning policy.

He said: "What we have now is a system out of control. I hope members on Monday will have the chance to get control back. They will be asking if they have any control, or is the Government driving this?"

The Seera report suggests that it wants Green Belt boundaries to be redrawn to accommodate thousands of new homes. The county council sent its final submission to Seera six days ago, calling for the housing to go in Didcot and Bicester.

Oxford City Council leader Alex Hollingsworth said: "Keith Mitchell cannot complain that the system is out of control when he is meant to be in charge of it. I think the problem is that, as county council leader and chairman of the regional planning committee, he is wearing too many hats."

Mr Hollingsworth, also a member of the regional planning committee, said he welcomed Seera's support for the city's Green Belt proposals.