The "fire practice pond" at Upper Heyford, which was used by the US Air Force until the the end of the last century

Chemical contamination at a former RAF base earmarked for 9,000 homes is the worst found in the UK, a report has said.

Testing at RAF Upper Heyford carried out on behalf of a developer found "unacceptable" levels of polyfluoroalkyl substances (PFAS), referred to as forever chemicals.

Fears have been raised previously that the site could be the source of pollution in nearby waterways, after earlier testing by campaigners and the Environment Agency.

Paul Silver, chief executive of developer Dorchester Living, said separate soil samples taken from residential areas showed the area was "safe for use".

PFAS are a group of thousands of man-made chemicals, some of which can cause cancer, which are often referred to as forever chemicals because they do not break down easily.

The results of the site investigations were uploaded to Cherwell District Council's website as part of a planning application.

The author of the report said they were higher than the village of Bentham, Yorkshire, "determined as having the highest level of PFAS in the UK".

The Environment Agency (EA) said military sites and airports were hotspots for PFAS, which were used extensively in firefighting foams for decades.

At RAF Upper Heyford, firefighters would practice putting out an aeroplane set on fire above a "pond" of fuel.

This training area was found to be "the most significant ongoing source of PFAS contamination identified".

Another report into ground and surface water found contamination was "widespread" at the site, with all samples exceeding environmental standards.

Subsequent independent testing by Gallos Brook Environmental Group found elevated levels of the chemicals in more than a dozen streams that flow from beneath the base.

Leigh Radwell has lived near the former military base for 16 years, but now says she hates living there

The results have prompted concerns from residents about existing and approved developments near the site, including a primary school.

Groundwater and surface water results from the school site in another report showed PFAS exceeded safe levels by environmental quality standards.

Calum Miller, MP for Bicester and Woodstock, said: "The most important thing is to understand fully what level of contamination, if any, there is in that area.

"And in the case of a primary school that people have real confidence that it's a safe environment for children."

The BBC has spoken to residents living near the site who would like their blood tested to determine if they have been disproportionately exposed.

One of them, Leigh Radwell, said she was concerned for her health after eating vegetables from her garden.

She said: "My little countryside haven and my dream of growing my own veg and having chickens and supporting wildlife is ruined.

Helen Christie, from Gallos Brook Environmental Group, said the results confirmed what campaigners had been saying: "That the site is contaminated."

But she said the testing done so far had been "inadequate".

"The duty of care now must be towards the 1,300 houses already built and those living in the surrounding areas," she added.

The report carried out for Dorchester Living said the PFAS contamination could be managed through a phased remediation approach.

CEO Paul Silver said: "This testing was the first step and an outline strategy for further investigation has been submitted as part of the planning application.

"We anticipate that this will include further investigation work on a phased basis with any necessary remediation to be secured through the planning process."

He continued: "The levels of contamination found on site are significantly lower than we had expected given its historic use. Soil samples taken from residential areas show that homes are safe for use"

The results of these further tests have not been made public.

Silver added: "We continue to recognise our responsibilities as a landowner and developer and are continuing to work with the Cherwell District Council, Environment Agency and other relevant government bodies."

The local authority previously called on the government to support it on the issue and a working group has been set up alongside the developer and the Environment Agency.

Cherwell District Council has been approached for comment.

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