Three English water companies face fines totalling £168million after an investigation found them guilty of sewage discharge failures.

Ofwat is proposing fines of £104million for Thames Water, £47million for Yorkshire Water and £17million for Northumbrian Water after the watchdog's biggest-ever probe. 

The water industry regulator found the firms had caused harm to the environment and their customers by regularly releasing sewage into rivers and seas rather than in 'exceptional circumstances' as the law allows.

It also found a failure to sufficiently upgrade assets to meet changing local needs and said they were 'slow to understand' the extent of their duties to limit pollution from storm overflows.

Ofwat suggested they did not properly operate and maintain their wastewater treatment works, given the 'strong correlation' between the steep spill levels and operational concerns at wastewater treatment sites.

The regulator will consult on the size of the fines before ordering the water businesses to pay them, as well as enforcement orders requiring each of them to deal with the problems it has uncovered.

Debt-riddled Thames Water's fine equates to 9 per cent of its annual turnover, while the figures for Yorkshire Water and Northumbrian Water are 7 and 5 per cent, respectively.

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.

Britain's water sector has faced immense criticism from politicians and environmental campaigners in recent years amid growing instances of sewage spills. 

According to the Environment Agency, water companies were responsible for spills in England more than doubling from 1.75 million hours in 2022 to 3.6 million hours last year.

Water UK, the trade association for the UK's water industry, blamed the increase on higher rainfall, which is the primary driver of storm overflows.

However, the Environment Agency said this 'does not affect water companies' responsibility to manage storm overflows in line with legal requirements.'

To clean up the country's rivers and waterways, Ofwat ruled in July that English and Welsh water firms could spend £88billion between 2025 and 2030 on infrastructure upgrades.

Funding for these improvements will come from hiking household water bills by an average of £94 over the five years, excluding inflation.