Oxford City Council is looking to annex enough Green Belt land to build at least 12,000 homes as part of a proposed urban extension.

The city council has confirmed it is now interested in moving the local authority boundaries so that it controls 530 hectares of land south of Greater Leys.

The land is under the control of South Oxfordshire District Council.

The move has outraged Green Belt campaigners and South Oxfordshire district councillors as the area is almost three times the 180 hectares that it was assumed the city council would seek to bring under its control.

The city council has long expressed its desire to build 4,000 homes on land south of Grenoble Road, near the Kassam Stadium.

It had been assumed that the city council would seek to move the local authority boundaries only so far as to allow them to build these homes.

But documents seen by The Oxford Times reveal that the land the city has asked to be allowed to annex in its submission to the Boundary Committee for England is much larger.

The director of the Oxfordshire branch of the Campaign to Protect Rural England, Dr Helena Whall, said: "Oxford City Council's intentions are now clear. It wants to expand exponentially and develop Oxford's Green Belt in stages.

"It is not bidding for 530 hectares of Oxford's Green Belt for a limited development of 4,000 affordable homes and to protect what remains of the Green Belt.

"It is bidding for this land because it wants to build, over time, more and more homes on Oxford's Green Belt.

"If this becomes part of the city, there's no stopping them. They could erect 12,000 homes comfortably, but we think they could build up to 20,000 homes on the site if they wanted."

Charles Stanley, 45, a resident of the nearby village of Toot Baldon said: "If they manage to move the boundary to include all this land in years to come they will be building on it. That would ruin our village."

The land that the city council is seeking to annex is largely owned by itself, Magdalen College and Thames Water.

A decision is expected from the Boundary Committee for England next year.

City council deputy leader Ed Turner, the executive member for housing and strategic planning, said: "We wanted to include all this land in the review because the worst scenario for us would have been if the review said the most appropriate land for development was outside what we had applied for.

"We want to see this new development protected by the Green Belt and protect the land for the future.

"It's unthinkable the entire area will be developed. "

But Mr Turner said he could not guarantee that more than the 4,000 proposed homes would be built in the future.

He said: "Some people would say if there is more available land we should build on it, but there are no current plans to build any further homes.

"This is about lifting people out of some miserable conditions and it shouldn't be seen as a threat."

South Oxfordshire District Council leader Ann Ducker accused the city council of being "sneaky".