The campaigners who inspired Dirty Business drama

One of the campaigners who inspired Channel 4's new docudrama Dirty Business says the pollution of Britain's waterways has had "tragic and upsetting" consequences.

Ash Smith, who lives in Oxfordshire, began investigating why stretches of the River Windrush in the Cotswolds were becoming polluted – alongside his fellow campaigner Peter Hammond – in 2016.

The pair are now the focus of Dirty Business, which is partly based on their decade‑long investigation into England's water companies.

It tells the real stories of whistleblowers and victims who believe their lives have been destroyed after encountering sewage‑polluted water.

"The stories are real, they're about real people, and some of it is so tragic and upsetting," Ash said.

He said he first noticed issues with the Windrush, which is a tributary of the Thames, shortly after moving to west Oxfordshire.

"I've spent my life around rivers, I know what rivers should look like when they're healthy and the Windrush had a fantastic name, a beautiful reputation and I saw it and I thought that's not right," he said.

"Within two years the weed went and the river was looking miserable."

The campaigner, who co-founded the Windrush Against Sewage Pollution group, said: "I then started asking the questions and using the freedom of information law to dig a little deeper and [what I found] is concerning and it's disturbing."

What began for Ash and Peter as a concern over their local river became a decade long battle to hold water companies to account over sewage discharges.

"We've concentrated on being accurate, on being truthful and not exaggerating - because you don't have to - it's shocking enough," Ash said.

"In fact, every time we thought we'd got something that was really bad it actually turned out to be far worse.

Former police officer Ash and Peter, who had been an Oxford University maths professor, have spent years investigating the sewage discharges and have built up a picture of environmental catastrophe in the country's waterways.

"We're in a terrible state and that has to be fixed really quickly - but first of all we need to get to the heart of the problem that caused it," he said.

The story of the pair's sleuthing has now been turned into the three-part Channel 4 series, which aired this week.

It has already drawn comparisons to 2024's Mr Bates vs The Post Office, with The Guardian saying that series demonstrated that "television drama can suddenly intensify public disgust at a scandal, forcing official attitudes to change".

"If this doesn't do it, perhaps nothing will," Jack Seale added in his five-star review of the series.

Ash, who is played in the show by Harry Potter star David Thewlis, said he hoped the series would make it clear "we're in the middle of something".

"This is not like an account of something that happened - it's an ongoing thing," he said.

"We've always been about informing the public and getting to the tipping point where enough members of the public know what is wrong and demand for it to be changed.

"It's 2026, we can afford to do it, we've paid to do it, we've paid easily enough money to do this properly and it's been diverted in what I think is a huge scam."

Sewage discharges are legally permitted during heavy rainfall because combined sewer overflows act as a "safety valve," preventing the sewer network from backing up and flooding homes, roads and businesses when the system is overwhelmed.

Last year the government pledged to halve the number of times sewage is discharged by water companies.

It came after Thames Water received a record £122.7m fine for breaching rules over sewage spills and shareholder payouts.

The company has previously said it takes its responsibility towards the environment seriously.

The BBC has contacted Thames Water for an updated comment.

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