Jeremy Corbyn has acknowledged that Labour faces "a challenge on a historic scale" to win the June 8 General Election after a disastrous set of local ballots which saw the party shed 320 councillors and lose control of strongholds including Glasgow.
But he insisted that the gap separating Labour from the Conservatives is "not as great as the pundits are saying", as he urged supporters to campaign hard to win over millions of voters who he said were still "sceptical and undecided, not sure which way to turn".
The Labour leader promised that if he wins power on June 8, there will be "a reckoning" with big businesses and bankers who he accused of crashing the economy, stripping industrial assets and ripping off workers and consumers.
Mr Corbyn told supporters in Leicester that the General Election represented "a great opportunity ... to create a society in which people are no longer held back by a system that is rigged for the rich. A chance to rebuild Britain for the many, not the few".
Acknowledging that Friday's results were "disappointing", he told activists: "We know this is no small task - it is a challenge on a historic scale. But we, the whole Labour movement and the British people, can't afford not to seize our moment.
"We have five weeks to win the General Election so we can fundamentally transform Britain for the many, not the few."
Mr Corbyn turned his sights on tax cheats and rip-off businesses as he told supporters: "When Labour wins there will be a reckoning for those who thought they could get away with asset stripping our industry, crashing our economy through their greed and ripping off workers and consumers.
"It makes me angry. It makes me really angry. And I know it makes the people of Britain angry too.
"Today, I say to tax cheats, the rip-off bosses, the greedy bankers: 'Enough is enough. The people of Britain are taking our money back.'"
The June 8 election could be "a great and proud moment in our national story", he told supporters.
"Don't wake on up on June 9 to see celebrations from the tax cheats, the press barons, the greedy bankers, Philip Green, the Southern Rail directors and crooked bankers that take our wealth, who have got away with it because the party they own, the Conservative Party, has won," he said.
"We have five weeks to ruin their party. We have five weeks to have a chance to take our money back. We have five weeks to win so we can transform Britain for the many, not the few."
Mr Corbyn won cheers from supporters as he repeated his challenge to Prime Minister Theresa May to face him in a televised leadership debate.
And he challenged her central election claim that she offers voters strong leadership, arguing that he had shown strength in his campaigns against the Iraq war and privatisation and for better public services and a fairer society.
"Strength is holding on to what you believe in," said Mr Corbyn.
"Standing up for the many against the few means a struggle against the odds.
"Looking out for the few is easy; winning for the many is hard.
"I have a message for Theresa May: If you feel the need to go on about what a great leader you are, then show it by debating with me in this election campaign. We are for the many, you're for the few."
Asked if he was contemplating resigning, Mr Corbyn said: "No, because I'm busy out campaigning to win the General Election on June 8.
"Of course I'm disappointed in the election results on Thursday, but we're out there giving the message of how the economy and our society could be very, very different."
He said there was a real choice at this election between Labour and the Conservatives, as he accused the Tories of "megaphone diplomacy" and making "absurd claims about what the EU is or isn't doing to the British election" over Brexit.
Mr Corbyn later gave a speech to dozens of party activists in a village hall in the Derby North constituency, which the Conservatives won by just 41 votes at the last general election.
He hit out at Tory cuts to the welfare system which could mean the need to "industrialise" food banks, as well as suggesting their plans for grammar schools would divide children into "sheeps and goats".
Mr Corbyn also urged campaigners to get people registered to vote, saying two million young people were still not registered.