The Labour Party now can boast 800,000 members, a shadow cabinet member has claimed. Richard Burgon, the shadow justice secretary and an ally of Jeremy Corbyn, said the 150,000 new members joined since Thursday's general election on 8 June, inspired by the unprecedented revival in party's popularity.
Paul Mason, a former BBC journalist, also made the claim on Twitter in the wake of the election result, which saw Labour gain 30 seats and win 40% of the popular vote to deny the Conservatives of a majority in the House of Commons.
But a Labour spokesperson refused to confirm or deny the figures when approached by IBTimes UK, stating that the party did not comment on membership figures.
The previous peak of Labour's membership under Corbyn was more than 554,000 people, while the Conservative Party membership was under 150,000 in late 2016.
The left-wing leader has called on Prime Minister Theresa May to quit Number 10 after the election and told the BBC's Andrew Marr that he is ready for another election in 2017.
"This election wasn't just about Brexit – there was something very different about it. It was challenging an economic consensus, which has impoverished so many people," he said.
Corbyn also promised to "reach out" across his party in a bid to unite Labour as Theresa May's premiership looks increasingly uncertain.
"Ever since I became leader I reached out and there have been one or two difficulties at time in the parliamentary Labour Party, but let's put that behind us," Corbyn said.
"The issue is the party came together behind a brilliant manifesto...came together for a result that you and nobody else expected."
Elsewhere, the 22,000 strong pro-Corbyn pressure group Momentum has revealed how it engaged with young voters ahead of the 8 June vote.
The organisation claimed to have reached 30% of UK Facebook users with viral videos. One video, "Daddy, why do you hate me?", has been viewed more than 7.6 million times on the social media site. Momentum also used WhatsApp messages to contact 400,000 voters on election day.
"During this campaign Momentum proved itself to be a powerful force which can help Labour win seats and increase majorities," said Emma Rees, a national organiser for Momentum.
"We're going to continue on a permanent election footing, ramp up our activity in newly marginal seats and embed the Labour Party in communities outside of election time."