Sir Keir Starmer claimed there was a “change in the air”, with Labour ready to be form the next government after 12 years of Tory failure.
The Labour leader, who has set out plans for a green energy revolution to boost economic growth as a counter to the “trickle down” policies set out by Liz Truss and Kwasi Kwarteng.
Sir Keir used speeches to activists on the eve of the Labour conference opening in Liverpool to denounce the “shower” in Downing Street, who he accused of “taking the piss” by offering tax cuts to the rich while giving less support to poorer households.
The Labour leader pledged to double the amount of onshore wind, triple solar and more than quadruple offshore wind power by 2030, according to details announced in The Observer ahead of the party’s annual conference.
The creation of a net zero carbon, self-sufficient electricity network would lead to permanently lower energy bills and independence from nations such as Russia, according to Labour.
The move could also create half a million jobs and make the UK the first country to have a zero-emission power system.
In a speech to activists, Sir Keir said the Chancellor’s admission of Tory economic failure would be hung “around their necks” in the next election campaign.
He said: “There’s a change in the air. There’s an atmosphere, there’s a sense that Labour is ready to deliver.
“And don’t we need change after 12 years of this shower, 12 years of failure under this government, wages stagnant for 10 years, public services on their knees.”
It is already clear that the Chancellor’s mini-budget on Friday will set the dividing lines for the next general election, with Sir Keir telling Labour supporters: “I didn’t agree with almost anything he said in that financial statement yesterday apart from his opening sentence, when he said there’s a ‘vicious cycle of stagnation’.
“He’s right about that and it’s their vicious cycle of stagnation. That is the verdict on 12 years of Tory government, a vicious cycle of stagnation and we need to hang that around their necks.”
The former director of public prosecutions said it was good when “somebody who is caught red handed actually pleads guilty”.
He said the Government’s “driving ideology” is now to “make the rich richer and do nothing for working people”.
“If you earn a million pounds, yesterday, you got a £55,000 pounds tax cut, enough to pay for a nurse,” he said.
“It’s not trickle down, it’s taking the piss.”
The Labour leader’s relationship with union chiefs has been strained by his refusal to offer full-throated support for the wave of strikes triggered by the cost-of-living crisis.
But he insisted he would lead the “most pro-trade union Labour government you have ever seen”, promising a Green Paper on workplace rights within 100 days of an election victory.
The conference is vital for Sir Keir to present himself as an alternative prime minister to Ms Truss, with the next election expected in 2024.
Sharon Graham, general secretary of the Unite union, told the BBC the Labour leader should “be bolder” in his economic policy and not “stand still” in order to win power.
The conference will formally begin on Sunday, with tributes to the Queen and a rendition of the national anthem.