Mr McDonnell believes Theresa May will step down in early Summer sparking a Conservative leadership election with the winner calling an Autumn election. And the shadow chancellor expects to have the keys to the Treasury after a Labour victory saying he “bloody hopes” to be in power.
He told Tortoise Media: “I am working on October. We have been aware of the prospect of an early election for some time now but I think the timetable is this.
“If Theresa May goes after May 22 they will go straight into a leadership election. The timetable would be mid-July for that new leader to be in place.
“The new leader goes off to party conference and then there’s a general election.
“I am working back from dates in October and getting our team and the campaign team ready and all the prep for government work is being done as well. Yes, we think it will be October.”
The Hayes MP spend decades in the political wilderness after Tony Blair became Labour leader in 1994 only to make an improbable entry to front bench politics after Jeremy Corbyn clinched the Labour leadership in September 2015.
Conservative big beasts are currently preparing a leadership tilt include Boris Johnson, Michael Gove, Sajid Javid and Jeremy Hunt.
Despite previously losing the confidence of his MPs under Labour leadership rules it is almost certain he will be in charge of the party during a General Election later this year.
Mr McDonnell’s confident prediction comes as Theresa May was put under more pressure today.
Conservative Party Brexiteer Mark Francois wrote to the chairman of the powerful backbench 1922 Committee demanding an indicative confidence vote in the PM on Wednesday.
However, a formal vote of confidence in Mrs May as Conservative leader cannot be held until December, after she survived an earlier attempt to oust her by 200 votes to 117.
Mr Francois wrote: “We simply cannot go on like this, with a weak leader, a riven Cabinet and a party in despair.
“I believe Theresa May has been a failure as leader of our party, which she now threatens to destroy. Hers is a classic example of hubris – and after hubris comes nemesis.”
Meanwhile, Labour leader Jeremy Corbyn was due to meet Sinn Fein leaders party president Mary Lou McDonald and vice-president Michelle O’Neill this afternoon.
The Sinn Fein pair will also meet Northern Ireland Secretary Karen Bradley and a number of SNP MPs at Westminster.
Mrs McDonald said: ”We will set out again the very clear need to protect Irish interests and make it very, very clear that whatever way Brexit lands, deal or no deal, that Irish interests have to be protected.
“Our peace process, our all-Ireland economy, crucially our citizens’ rights, cannot be the collateral damage to the Tory Brexit.”