The UK's opposition Labour Party would create a publicly owned energy company in its first year in power, Sir Keir Starmer has pledged.
The new policy was announced in the leader's speech to the Labour conference in Liverpool on Tuesday to sustained applause.
Sir Keir said Great British Energy, a new company, would take advantage of opportunities for clean power.
Of its public ownership, he said it would provide "British power to the British people".
Sir Keir's speech was mainly focused on criticism of the governing Conservatives' tax cutting mini-budget, which "crashed the economy" to offer tax cuts to the rich.
He was speaking after a new YouGov survey released on Tuesday put Labour 17 points ahead of the Tories, the party's greatest lead since the firm started polling in 2001.
Mr Starmer told delegates the public should "never forgive" the Conservatives for the financial turmoil their mini-budget caused. The measures announced by Chancellor Kwasi Kwarteng on Friday led to the pound falling to its lowest ever level against the dollar on Monday.
He said what the country had seen in the past few days was "unprecedented".
"They've crashed the pound. And for what?" he asked.
"Higher interest rates. Higher inflation. Higher borrowing. And for what?
"Not for you. Not for working people. For tax cuts for the richest 1 per cent in our society.
"Don't forget. Don't forgive."
Everyone earning less than £155,000 ($166,778) had lost out with the plan, he said. He added that the mini budget had left a "Britain all at sea, where a cloud of anxiety hangs over working people".
"At moments of uncertainty like this, we must provide clear leadership," the Labour leader said.
"We must stand with working people. Meet their ambitions for real change. Walk towards a better future and build a new Britain, together."
Sir Keir said the Tories "haven't just failed to fix the roof, they've ripped out the foundations, smashed through the windows and now they've blown the doors off for good measure".
He promised a Labour government would "get us out of this endless cycle of crisis" with a "fresh start, a new set of priorities and a new way of governing".
He spoke about growing up in a "pebble-dash semi" and said he remembers rising prices.
Labour's first step should be to tackle the cost of living crisis affecting the country, he said.
He said the Ukraine war was the immediate cause of rising prices, but stressed that Labour stood by the Ukrainians and would “never allow imperialism to succeed”.
"Slava Ukraini," he added.
Sir Keir said the war had left the UK unprepared for the economic fallout and soaring energy bills.
"The war didn't ban onshore wind. The war didn't scrap home insulation. The war didn't stall British nuclear energy. The Tories did that."
He said this was "Labour's moment".
