As Labour teetered on the brink of all-out civil war, Mr McDonnell won loud cheers at a pro-Corbyn fundraising event as he denounced those seeking to force a change at the top of the party.
The contest has been triggered by a challenge against the leader from ex-shadow minister Angela Eagle, who criticised Mr Corbyn for failing to connect with labour voters.
File image of Jeremy Corbyn.
This Branch notes that Jeremy Corbyn was recently elected by members on the first round with 59.5% of the vote.
She said there should be no legal challenge to the NEC's decision but warned that Labour risks electoral wipeout in the north at the hands of Ukip, similar to that it has suffered in Scotland if Mr Corbyn remains leader. I think that's more important than any of the details about how the contest will go forward.
Eagle called on Corbyn to rein in his supporters, saying attacks such as the vandalising of her office were "being done in his name, and he needs to get control of the people who are supporting him and make certain that this behaviour stops and stops now".
Ms Eagle has already obtained the signatures, while the National Executive Committee ruled on Tuesday that Mr Corbyn did not need them.
Steve McCabe, MP for Birmingham Selly Oak, claimed that Jeremy Corbyn was leading the party "over a cliff", while Jack Dromey, Labour MP for Birmingham Erdington, said the party was heading for a "crushing defeat" under Mr Corbyn's leadership. I think we now need a real debate about the future direction of our party.
"The procedural rules of the leadership election state that no CLP (Constituency Labour Party) meetings may be held during the contest". As more than 100,000 new members joined in the weeks following the referendum, moderates feared that their support could have been dwarfed by this phenomenon again.
"I joined Labour because of Corbyn, the MPs' action is making me question my membership of the party."Even if Corbyn hangs on what's going to happen when he comes up against the civil service and the establishment?"
"Following the recent Brighton and Hove AGM, many complaints and reports of concern have been made to the National Labour Party".
"I am considering leaving the party now as I feel I have been cheated".
When quizzed about policy differences between himself and Ms Eagle, Mr Smith said again made the point he would call for another vote on Britain's European Union membership.
"Let's be clear, all harassment and intimidation is absolutely wrong and doesn't have a place in politics - as Jeremy Corbyn has repeatedly said and Momentum repeatedly says", said Mr Schneider.