In addition to the proposed sewage dumping fines, Ofwat plans to impose enforcement orders to require each company to rectify immediately the problems it has identified, promising a wave of fast-tracked sewage treatment works investment.

Ofwat said the companies would not be able to recover the money for penalties from customers to ensure they are not charged twice where extra maintenance is required.

These penalties are separate to the commitments that have been set out as part of PR24 draft determinations for all wastewater companies which will see £9.5bn overall enhancement expenditure for storm overflow improvements to meet their new performance commitment targets.

The regulator found the companies had failed to upgrade assets, where necessary, and routinely released untreated wastewater from storm overflows rather than only in exceptional circumstances.

Companies will not be able to recover the money for any proposed penalties from customers and Ofwat will ensure that customers are not charged twice where additional maintenance is required.

The penalties proposed for consultation will see Thames Water fined £104m, Yorkshire Water fined £47m and Northumbrian Water fined £17m.

Ofwat’s Chief Executive David Black said: “The level of penalties we intend to impose signals both the severity of the failings and our determination to take action to ensure water companies do more to deliver cleaner rivers and seas.

“These companies need to move at pace to put things right and meet their obligations to protect customers and the environment. They also need to transform how they look after the environment and to focus on doing better in the future.

“Looking to the future we want transform companies’ performance under our new price control that starts in April next year, so we reduce spills from sewage overflows by 44 per cent by 2030 compared to 2021 levels.”