UK water companies have apologised for dumping billions of litres of sewage and pledged to invest £10bn to reduce waste outflows in an announcement that has been dismissed by environmental campaigners.

Trade body Water UK issued the apology for polluting rivers, lakes and coastal waters in England and Wales in an open letter on Thursday. “The message from the water and sewage industry today is clear: we are sorry,” wrote Ruth Kelly, the former Labour cabinet minister who is now head of Water UK.

However, campaigner Feargal Sharkey condemned the pledge as “vacuous” and “empty”. The former pop star, who has become a leading critic of sewage pollution, said the “£10bn does not exist”.

The amount still needs to be agreed by regulator Ofwat and would be borrowed by water companies and paid for by an increase in customer bills.

Kelly argued that customers were willing to pay for the increased investment but acknowledged that “more should have been done to address the issue of spillages sooner and the public is right to be upset about the current quality of our rivers and beaches”. She added: “We have listened and have an unprecedented plan to start to put it right.”

The apology comes as water and sewage companies in England and Wales face the biggest wave of public protests since privatisation 34 years ago.

The regional water monopolies are accused of paying out billions of pounds of dividends and hefty pay packages for executives at the same time as tipping unknown quantities of storm water and sewage into coastal waters and rivers.

“This problem cannot be fixed overnight, but we are determined to do everything we can to transform our rivers and seas in the way we all want to see,” Kelly wrote.

Labour condemned the water companies’ proposal for passing the bill on to consumers. Shadow environment secretary Jim McMahon told Sky News: “We can’t allow in a cost of living crisis for families to take the burden of that because water companies still think they can carry on business as usual.”

He criticised ministers for effectively “legalising” sewage spills, despite having the “levers of power” to outlaw them as Labour has pledged to do.

Last week the chief executives of Yorkshire Water, Thames Water and South West Water declined their bonuses in an acknowledgment of the public anger over sewage pollution.

About a fifth of treated water across the industry is lost in leakage while just 16 per cent of rivers, lakes and costal waters meet the minimum standards for “good” ecological status, according to official figures.