Labour launched a full-frontal attack on the privatised water industry last night, accusing companies of paying out the “scandalous” sum of £13.5bn in dividends to shareholders since 2010, while claiming huge tax breaks and forcing up prices for millions of customers.

The assault by shadow chancellor John McDonnell came as he pledged total, “permanent” and cost-free renationalisation of water, energy and rail if Labour won power at the next election. The three privatisations in the 1980s and 1990s became hallmarks of the Tory governments of Margaret Thatcher and John Major.

The dramatic intervention – which stunned the companies involved – was the strongest denunciation yet by Jeremy Corbyn’s Labour of the privatisation programme that has become part of the British political landscape of the last 40 years.

The Conservative party and the Confederation of British Industry both condemned McDonnell’s comments. The CBI said Labour’s renationalisation agenda would “wind the clock back on our economy” while chief secretary to the Treasury Liz Truss warned that placing politicians in charge of public utilities “didn’t work last time and won’t work this time”.

McDonnell told the Observer that water companies could not even claim to offer choice to customers but instead operated regional monopolies, and were therefore able to increase prices without the risk of losing out to competitors, as well as “load up debt” while paying out huge dividends to shareholders.

“It is a national scandal that since 2010 these companies have paid billions to their shareholders, almost all their profits, whilst receiving more in tax credits than they paid in tax,” he said. “These companies operate regional monopolies which have profited at the expense of consumers who have no choice in who supplies their water.

“The next Labour government will call an end to the privatisation of our public sector, and call time on the water companies, who have a stranglehold over working households. Instead, Labour will replace this dysfunctional system with a network of regional, publicly owned water companies.”

Citing figures from the National Audit Office, the shadow chancellor said water bills had risen by 40% in real terms since privatisation of the industry in 1989. In 2016-17, the forecast average for water bills was £389 per household. McDonnell claimed that in 2017, privatised water companies paid out a total £1.6bn to their shareholders. Since 2010, the total was £13.5bn.

Michael Roberts, the chief executive of Water UK, which represents private water companies, said McDonnell was completely mistaken: “It’s wrong for Labour to suggest that our water system is broken. Water companies secure capital provided by lenders and shareholders, who need water companies to make a return in order to finance significant improvements to the industry.

“Under public ownership, the water sector in England was starved of cash and standards were poor. Private companies have instead invested heavily to reduce leakage, improve drinking water quality, and protect the environment – and they continue to invest £8 billion each year in even better services. In real terms, bills are roughly where they were 20 years ago and will be falling over the next few years.”

Meanwhile, at a conference on alternative models of ownership in London, Corbyn backed the nationalisation of Britain’s energy system as a way to tackle climate change. He said that “the challenge of climate change and the threat of climate catastrophe requires us to be at least as radical” as the 1945 Labour government that created the National Health Service. Corbyn said that Labour would back a “great wave of change across the world in favour of public, democratic ownership and control of our services and utilities.

“We can put Britain at the forefront of the wave of change across the world in favour of public, democratic ownership and control of our services and utilities,” he said.

“From India to Canada, countries across the world are waking up to the fact that privatisation has failed, and taking back control of their public services,” he added.

The water industry was privatised in 1989, transferring the assets and personnel of the 10 water authorities into limited companies. Capital was raised by floating the companies on the stock exchange, accompanied by a one-off injection of public capital, the write-off of government debt and the provision of capital tax allowances.