Labour crisis: Alan Sugar and Alastair Campbell lead anti-Corbyn campaign

Lord Alan Sugar and Alastair Campbell are two of the best-known names backing an online campaign to oust Jeremy Corbyn as Labour leader. The former Number 10 communications chief and the ex-Labour peer are urging hundreds of thousands of their followers on social media site Twitter to sign a 'Saving Labour' petition.

The form sends an automated email to a backer's Labour MP or chair of the parliamentary Labour Party, John Cryer, if they do not have one. "If you agree that it is time for Jeremy Corbyn to step aside for the good of the country, add your name here to email your MP to show your support," a statement on the website says.

The campaign is designed to drum-up support among Labour MPs to back a motion of no confidence against the left-wing leader.

MPs are casting their vote this afternoon (28 June) after a string of MPs resigned from Corbyn's shadow cabinet after Hilary Benn was sacked as foreign secretary and many Labour heartlands across England and Wales backed a Leave vote in the EU referendum.

But despite the mass resignations and increasing pressure against him, Corbyn, who won the 2015 Labour leadership election with almost 60% of the vote, has vowed to stay on and run in another contest for the top job.

Campbell, a co-architect of New Labour, wrote in an IBTimes UK comment piece: "A sect has taken control of one of the two most important national political organisations. If [Corbyn] was a decent man, he would do the decent thing and go, and let someone who can lead take on the role of leadership.

"If he remains, fighting harder for this remain than the one he should have fought for, then he will earn his place in history – as the man who split and possibly destroyed the Labour Party in an act of vandalism and vanity.

"In this, he is the Labour version of Boris Johnson who, out of ego, ambition and vanity, has risked the destruction of the country he claims to love and claims he could be capable of leading."

Campbell is also encouraging people to join Labour so that they can vote against the left-winger. "If you think Corbyn has to go, join the Labour Party, and help make that happen so that it can become a proper functioning campaigning party again, not a hard left sect and vanity project, as a general election nears," he said.

Labour's 2015 contest gave people the opportunity to sign up for the one-off fee of £3 and vote in the leadership, deputy leadership and Mayor of London nominee election. The election also used the one-member, one-vote system for the first time. The party currently offers varying membership rates, but a standard sign-up costs £3.92 month.

A Labour spokeswoman refused to clarify to IBTimes UK how long, if at all, a person would have to be a member before being eligible to vote in a leadership election. But a statement on the party's membership section says: "You'll be eligible to vote in leadership elections, you can help shape party policy, you can attend local meetings and you can even stand as a candidate."