Popular holiday resorts in Cornwall and the New Forest, as well as popular bathing spots and habitats of rare wildlife were affected.

The move comes at a time when Sir Keir Starmer’s government is under pressure to tackle the sewage crisis, which has resulted in more than 450,000 sewage spills over more than four million hours last year.

Charles Watson, executive director of River Action, said the figures on suspected illegal oil spills showed a level of lawlessness in a broken system and called on the government to take radical action to end the practice.

“If anything showed the extent to which our sewage systems are broken, it would be this enormous number of potentially illegal dry discharges – on average about 20 a day,” he said.

“And if there is anything that proves the environmental damage caused by this widespread, unlawful water industry behaviour, it is the repeated pollution of the country’s most ecologically sensitive areas – including many of our areas of outstanding natural beauty.”

Ash Smith, of the campaign group Windrush Against Sewage Pollution, said the dry runoff figures showed the Environment Agency had allowed the problem to “spread out of control”.

“What can they be other than illegal?” he said. “The Environment Agency is an absolutely pathetic regulator when it comes to dealing with this.”

The Telegraph examined the start and end times of all sewage discharges in 2023, provided by England’s nine water and sewerage companies under a Freedom of Information Act (FoI) request.

The data from these requests were compared with weather data to find leaks that occurred within a three-day period without rain (so-called dry leaks).

In total, 881 dry leaks occurred in 22 of England’s 34 designated Areas of Outstanding Natural Beauty, with the potential to cause major environmental damage due to poor dilution of wastewater.