Thames Water has been hit with a ￡104mn regulatory fine for failing to manage its wastewater treatment works, piling further pressure on Britain’s biggest water utility, which is fighting for its financial survival.

Ofwat said Thames Water and two other companies — Yorkshire Water and Northumbrian Water — would be penalised for breaching licence conditions. They had failed to upgrade or adequately maintain and operate their wastewater treatment works, the regulator said.

As a result, the combined sewage overflows — which are designed to release a mixture of storm water and sewage into waterways in “exceptional circumstances” such as heavy rain — are frequently overwhelmed and “routinely” release sewage into rivers and seas, the regulator said.