Labour’s plans to bring services into public ownership would cost “absolutely nothing”, John McDonnell has said.

The shadow chancellor outlined an agenda to put public services “irreversibly in the hands of workers” so they could “never again be taken away”.

He told a Labour gathering in London that public ownership was not just a political decision but an “economic necessity”.

“It would be cost-neutral because you would be bringing into public ownership an asset,” McDonnell told Sky News.

“In addition to that, you would not just have an asset, that asset would give you income. Instead of that income going to shareholders, it would come to the taxpayer.”

Asked whether public ownership would cost “absolutely nothing”, he replied: “Exactly that”.

The shadow chancellor told Labour’s alternative models of ownership conference: “The next Labour government will put democratically owned and managed public services irreversibly in the hands of workers, and of those who rely on their work.

“We will do this not only because it’s right, not only because it’s the most efficient way of running them, but also because the most important protection of our public services for the long term is for everyone to have and feel ownership of them.

“We aren’t going to take back control of these industries in order to put them into the hands of a remote bureaucracy, but to put them into the hands of all of you – so that they can never again be taken away.”

The CBI’s managing director for people and infrastructure, Neil Carberry, said Labour’s calls for nationalisation would wind the clock back on the UK’s economy.

“If Labour turns its back on good collaboration between the government and the private sector, public services, infrastructure and taxpayers will ultimately pay the price,” he said.

McDonnell announced the creation of a working group to look at how cooperatives can grow, expand and access capital, and to decide which sectors should be prioritised in the expansion of cooperative ownership.

He accused the Conservatives of failing the UK. “Under the Tories, Britain is now seriously out of step with our international partners, failing to keep up with them,” he said.

“The Conservatives are intellectually bankrupt, caught between clinging on to the failing dogmas of the past and offering a pale imitation of the radical change which Jeremy Corbyn’s Labour party now offers.”

The chief secretary to the Treasury, Liz Truss said: “Independent reports show Labour’s renationalisation plan will cost taxpayers billions and lead to worse services for people.

“Labour would put politicians in charge of running everything from the phone lines to electricity supply, meaning people have nowhere to turn when things go wrong. That didn’t work last time and won’t work this time.”