Norfolk customers of Anglian Water could get millions of pounds in compensation if the company is found to have over-charged consumers in a landmark legal battle.
The firm is one of five UK water companies which appeared in court proceedings for the first time over allegations of under-reporting pollution incidents and over-charging customers as a result.
Anglian Water, Severn Trent Water, United Utilities Water, Yorkshire Water and Northumbrian Water are alleged to have failed to reveal the true scale of sewage discharges and spills made into UK waterways.
They are also alleged to have breached competition law because any under-reporting could have affected the price they could charge customers.
The claims are being brought by Professor Carolyn Roberts, a water resource management specialist, on behalf of an estimated 20 million affected customers.
Law firm Leigh Day, which is representing Prof Roberts, said households could receive a share of up to £800m in compensation if successful.
Legal representatives for the five firms appeared at the Competition Appeal Tribunal in London for a preliminary hearing in London on Tuesday.
Prof Roberts and the respondents already agreed the claims against all five firms should be heard together.
Industry regulator Ofwat, which is currently carrying out its own investigations into regulatory breaches, also attended the hearing amid questions over how the claims being brought by Prof Roberts might relate or interact with its own probes.
Mr Justice Marcus Smith set the date for a hearing to decide whether the claims are suitable to proceed as opt-out collective claims – where all affected customers are included in the claim unless they request to be removed – and approve Prof Roberts as the class representative in the week starting September 23.
But Mr Justice Marcus Smith also set the date for a second hearing from January 13 next year, to cover any extra issues due to the complex questions around Ofwat’s own investigations and powers under the Competition Act.
If certified, the claims can proceed to a full trial, which Leigh Day estimates will take at least two to three years.
Previously, a spokesman for Water UK, which represents companies like Anglian Water, said it was a "highly speculative claim" which was "entirely without merit".
Anglian Water has come under scrutiny over sewage problems in recent months - including at Gorleston and Mundesley.
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