The government and the water regulator broke the law by allowing sewage to be discharged outside of “exceptional circumstances”, according to the green watchdog.
Outlets called combined sewer overflows (CSOs) are only meant to be opened on rare occasions, such as during very heavy rain to stop sewage flooding back into homes and businesses.
But the Office for Environmental Protection said environment department Defra, water regulator Ofwat and the Environment Agency failed to give guidance, permits and enforcement for the use of CSOs in line with the law.
The findings come in a crucial week for the water industry.
Campaigners who made the complaint to the green watchdog said it showed pollution “plaguing” rivers would not be happening if the various bodies were doing their jobs properly.
Sewage discharges can cause diarrhoea, stomach cramps and fever for swimmers, as well as harming wildlife and ecosystems.
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The Office for Environmental Protection (OEP) has sent notices on what action must be taken to remedy the situation.
The various bodies have two months to respond, but a failure to take action could see them taken to court.
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“The core issue identified in our investigation is the circumstances in which the regulatory system allows untreated sewage discharges to take place,” said Helen Venn, the OEP’s chief regulatory officer.
“We interpret the law to mean that they should generally be permitted only in exceptional circumstances, such as during unusually heavy rainfall,” added Ms Venn.
“This is unless an assessment of the CSO concludes that the costs to address the issue would be disproportionate to the benefits gained.
“While the public authorities are now taking steps to ensure their approaches are aligned and reflective of the law, we have found that this has not always been the case.”
The OEP investigation did not include overflows at sewage treatment works – where the Environment Agency is now investigating companies for potential failures.
In response to the findings, an Ofwat spokesperson said it was “actively taking steps to remedy the issues”.
“We will continue to prioritise our enforcement investigation into all wastewater companies which started in 2021 to ensure that companies are meeting their environmental obligations,” they said.
A Labour spokesperson said “catastrophic policies” by the Tories had “left record levels of sewage pollution in Britain’s rivers, lakes and seas”.
They said they had now acted “decisively” to put water firms in special measures, with new powers to ban bonuses and bring back criminal charges.
An Environment Agency spokesperson said it had “made significant progress in addressing the issues identified by the OEP and are consulting on updates to our permitting approach and regulatory framework for storm overflows”.
People whose homes have been destroyed by the floods sweeping across parts of the UK over the past couple of days have been telling Sky News how they coped with the deluge.
In Lincolnshire, where a major incident has been declared, Terry, from Grantham, showed a Sky crew the aftermath of the deluge in his home, which was left under two feet of water.
“Everything’s gone,” he said, adding that he was “devastated”.
The first sign of trouble came at lunchtime on Monday, when his wife woke him and said there was water coming in [to the house], and “within a few minutes, the whole house was flooded”.
They rushed their belongings and pets upstairs, he said, as he revealed the damage to the flooded living room and kitchen, where the water mark was above a power socket.
Terry said the kitchen, where the floor was covered in sludge, smelled of mud and sewage, and their furniture and carpets were wrecked.
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They have no electricity and the food in the cupboards and freezer was “completely ruined”.
Graham Johnson, who lives in a boat with his wife and dog, in the village of Barrow upon Soar in Leicestershire, was in the pub on Monday night, before the water started to rise “rapidly”.
People living in a local caravan park were moved as a severe flood warning was issued.
Mr Johnson said he had gone out “for a couple of pints as usual and, the next thing we know, bingo”.
The couple feared their boat home was about to be swept towards the bridge.
“That’s our pride and joy, where we live, and we didn’t want to lose it,” he said, as he praised the “fantastic” emergency services, who rescued them and their dog after a nervy three-hour wait.
They were two of the 59 people rescued by firefighters in the county, where a major incident was declared and crews were called out to 160 flood-related incidents, the Fire Brigades Union (FBU) said.
Another Leicestershire resident whose home was inundated was Qasim Abdullah from Loughborough.
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Pictures taken by the Associated Press show him walking through almost knee-deep water in his living room.
In nearby Quorn, businesses have shut as the main high street has flooded for the second time in as many years.
Two of the pubs in particular have been damaged.
Last year, residents had to launch a crowd fundraiser to help pay for the costs of renovation. Not to mention soaring insurance premiums.
Indy Burmi, who owns a hair salon and restaurant, hasn’t suffered flooding, but said he’s had to close up and cancel all Tuesday’s reservations, as his clients simply can’t get into the village.
And, with more rain forecast, conditions could get even worse in the short term, while residents worry that an annual battle with rising water is now the new normal.
Elsewhere in the UK, the next danger is from ice forming on untreated surfaces after rain on Tuesday evening, the Met Office has said, as it issued a new warning for northern England and Wales from 5pm until midday on Wednesday.
The Royal Liverpool University Hospital has declared a critical incident due to “exceptionally high” demand on A&E and patients being admitted to wards.
The hospital said there had been a spike in people with flu and respiratory illnesses going to emergency departments in recent weeks.
A spokesperson for the hospital said it had a “comprehensive plan in place” and was “taking all the necessary actions to manage the challenging circumstances”.
“We are working with partner organisations to ensure those that are medically fit can leave hospital safely and at the earliest opportunity,” they added.
The hospital warned some people would experience delays as it prioritises the sickest patients.
People whose case isn’t an emergency are being asked to see their GP, pharmacy or walk-in centre – or call the 111 service for advice.
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The Royal Liverpool University Hospital is in the city centre and is the biggest hospital in Merseyside and Cheshire.
Declaring a critical incident can happen when a hospital is experiencing exceptional demand, or sometimes if there is a serious problem with staffing levels.
It indicates it can’t function as normal and allows it to take extra measures to protect patients, such as prioritising the most unwell people and getting support from other agencies.
It could last hours, a few days, or weeks if necessary.
A critical incident was also declared on Friday by the NHS Cornwall and Isles of Scilly Integrated Care Board.
It said it had seen almost four times as many inpatients compared with last year and urged people with flu to avoid going to A&E.