Secret court documents leaked to a prominent water campaigner suggest that more than eight out of ten sewage spills in England over the past two years could have been illegal — yet none have been punished.
Prof Peter Hammond, a retired academic whose work has been cited in Parliament and by economic regulator Ofwat, obtained a previously undisclosed definition of “heavy rain” from internal Environment Agency (EA) documents linked to a 2021 court case against Southern Water.
“Secret court papers reveal 86% of sewage spills may be illegal, says campaigner Prof Peter Hammond.”
UK law bans the release of raw sewage during “normal” weather, but until now the regulator had never clarified what that threshold was. Hammond used the newly revealed definition to analyse spill data from more than 350 storm overflow outlets — covering all nine English water companies and serving over 30 million people.
He found that about 86% of the hours when raw sewage was discharged occurred when there had not been heavy rain, meaning the spills were potentially illegal.
“The definition from the court papers shows that for more than 80% of the time sewage was being spilled, the weather was normal,” Hammond said, adding that the industry had been allowed to spill routinely with no consequences.
The analysis comes amid mounting public anger over the amount of raw sewage being released into England’s rivers, lakes and seas. The country’s sewage system often combines rainfall and waste in the same pipes, leading to overflows during heavy rain — but campaigners have long argued that water companies spill far too often.
Water companies and the EA rejected Hammond’s findings, insisting they are working to reduce spill numbers. But the leaking of the court documents has intensified scrutiny of a sector already under fire: a damning review published in June 2025 called for stronger regulation, and in March 2025 record numbers of illegal sewage spills were recorded in Windermere alone.
Hammond’s analysis raises urgent questions about how many past spills were unlawful — and why no enforcement action has been taken. With the regulator’s own internal definition now public, pressure is mounting for a reckoning over the true scale of illegal pollution.