Ofwat expands sewage probe to all wastewater companies in England and Wales

The regulator has also served formal notices on Dŵr Cymru Welsh Water and Hafren Dyfrdwy.

"The opening of these enforcement cases follows detailed analysis of information on companies’ environmental performance and data about how often these companies spill from storm overflows," it said.

"This has heightened Ofwat’s concerns that these companies may not be fulfilling their obligations to protect the environment and minimise pollution."

The addition of four more water firms means there are now enforcement activities underway against all 11 water and wastewater companies in England and Wales.

Enforcement cases against Anglian Water, Northumbrian Water, South West Water, Thames Water, Wessex Water, and Yorkshire Water were previously announced in 2022, with "extensive" investigations still ongoing. Meanwhile, Southern Water remains subject to enforcement monitoring following a previous enforcement case in 2019.

Ofwat chief executive David Black said: "This is the largest and most complex investigation Ofwat has undertaken. However, Ofwat is committed to concluding these cases as quickly as possible, so that the sector can focus on delivering the £88bn expenditure PR24 will unlock to deliver cleaner rivers and seas. As part of this package of investment £10bn is ear marked to tackle storm overflows with a target to reduce spills from storm overflows by 44%."

He noted that Severn Trent recently announced a programme to significantly reduce use of storm overflow.

"The investigation will consider both current and past performance and reflect on the steps companies are now taking in deciding if and what action is needed," Black added.