The water regulator has said it has "serious concerns" over Anglia Water's sewage treatment works.

The Water Services Regulation Authority (Ofwat) said concerns were raised after it received information suggesting "widespread shortcomings" in how water companies were running sewage treatment works.

Anglian Water, Northumbrian Water, Thames Water, Wessex Water and Yorkshire Water submitted reports in December which worried the regulator, Ofwat said.

Ofwat interim boss David Black said: "The data that emerged at the end of last year suggested widespread shortcomings in how water companies were running sewage treatment works.

"The first phase of our investigation suggests those concerns are credible.

"We have identified shortcomings in most water and wastewater companies and are continuing to investigate.

"But we have already seen enough in five companies to cause serious concern and warrant us taking further action."

The water regulator said that information it was sent in December raised one of several concerns for each company.

Either it reported a large number of wastewater treatment works which might not be meeting their environmental rules, raised concerns about how the company meets environmental obligations, or did not show the company's workings.

Mr Black added: "We will now dig deeper into what these five companies have been doing, with the prospect of formal enforcement against them if we find they are failing on obligations Ofwat enforces.

We will have further questions for all companies on this.

"In the meantime, we expect them to make quick progress in addressing any potential non-compliance they might have, whilst strengthening how they manage their environmental obligations as a whole."

Earlier this year MPs on the Environmental Audit Committee said that England's rivers had become a "chemical cocktail" of sewage, agricultural waste, and plastics.

Only one water company - Hafren Dyfrdwy - did not report any treatment works that potentially did not meet a specific set of rules in the environmental permits.

An Anglian Water spokeswoman said: "We will, of course, continue to support Ofwat with the information they request.

"We’ve been transparent throughout and the regulator could have asked us at any point for further detail, which we would have provided.

"We want the public to know they can trust Anglian Water, and that we take our environmental obligations very seriously.

"We’re already ahead of schedule delivering our £800m programme of environmental improvements between now and 2025, which is specifically targeted at areas where we know we can make a difference."