Richmond's MP has challenged Boris Johnson to properly fund the Environment Agency amid fears it is unable to tackle the pollution of waterways, such as Beverley Brook.

The brook was contaminated by what appears to a large oil spill on Friday and the resulting pollution has spread over 13km – 8 miles – to the Thames.

The historic brook, which has been at the centre of regeneration project led by Sir David Attenborough, runs through Wimbledon Common, Richmond Park and Barnes, past the renowned Wildfowl & Wetlands Trust site, to the Thames.

Thames Water staff have been cleaning sewer pipes around the area where the spill originated, which appears to by Pyl Brook in Morden, which is a tributary of Beverley Brook.

Separately, the Environment Agency has been carrying out a clean-up of the watercourse, which is home to a number of fish species and other wildlife.

The brook is also used by deer in Richmond Park and has been popular with dogs. Currently, pet owners are being advised to keep them out of the water.

Speaking at Prime Minister's Questions, the Richmond Park MP, Sarah Olney said: "Last Friday, it emerged there had been an oil spill in Beverley Brook, a river which flows through Richmond Park to the Thames.

"Black waste oil and iridescence can now be seen along 13 km of the watercourse, posing a serious threat to the fish and local wildlife.

"The Environment Agency are investigating, but they are understaffed and underfunded while also battling against water companies over sewage discharge."

She asked: "Will the government commit to strengthening the powers of the Office for Environmental Protection, as the Lib Dems tried to do to the Environment Bill, so that it is able to hold the government and other public authorities to account over environmental damage in the same way the European Commission was able to?"

The MP later said she was disappointed with Mr Johnson's response. He told the Commons: "I know what's behind her question, Mr Speaker.

"It's a desire to return to the jurisdiction of the European Union. What we want to do is make sure that we use our landmark Environment Bill to continue to improve the quality of our rivers and that's what we're doing."

The Environment Agency told Nub News: "Officers continue our response to this incident and our contractors have placed absorbent booms to contain the oil which entered the Beverly Brook over the weekend.

"Further reports suggest that traces of the oil have reached the River Thames and this is being closely monitored.

"We will continue to work with our contractors and our Field teams over the coming days in removing the oil, limiting any potential environmental impacts and investigating the source of the pollution.

"Members of the public should report pollution incidents to our free 24-hour Incident Hotline on 0800 807060."