The new Oxford children's hospital will only be able to open after Thames Water has carried out work to solve sewage problems in the area.

For decades, residents in Marston have complained of sewage flowing on to the streets during heavy rainfall.

On June 25, city councillors took the opportunity to ensure that improvement work would be carried out within the next three years.

They granted planning permission for the children's hospital, a three-storey unit at the John Radcliffe Hospital in Headington, which will be built by December 2005.

But as part of the approval, they imposed a condition which will make the upgrade of the sewerage system a legal requirement.

Both Thames Water and the Oxford Radcliffe Hospitals NHS Trust asked councillors not to impose the condition, saying it could create additional costs.

But councillors decided to go ahead, saying they did not trust the past performance of Thames Water.

Former Lord Mayor Maureen Christian, who represents Headington Hill and Northway ward, said Thames Water had failed to address the sewage problems in Northway and Ferry Road.

She added: "Even with mild rain, you can have open sewage, and for years we have been trying to get Thames Water to do something about it."

Thames Water's waste water director, Robin Clarke, said the company met trust representatives on June 6 and agreed to provide the necessary capacity for the new development by 2006.

After yesterday's meeting, Mr Clarke said he thought it unfair that councillors claimed Thames Water could not be trusted.

He added: "We don't think the planning condition is necessary because we have already agreed to carry out the necessary work."

Vickie Lamb, relocation project director for Oxford Radcliffe Hospitals NHS Trust, said a second planning application was now being submitted to the council for a bus lane off Osler Road through the hospital site.