Momentum is expected to go head-to-head with Labour’s biggest trade union backer in the battle for the party’s next general secretary, after a late-night conference call failed to persuade the grassroots group to rally around the Unite candidate.
Jon Lansman, the founder of Momentum, has told friends he is considering a bid to replace Iain McNicol, who is standing down, and is expected to announce his intentions on Tuesday.
Senior sources at the leftwing group, which has been a key backer of Jeremy Corbyn, said there was dissatisfaction that unions could in effect decide between themselves who would secure the position.
A source close to Lansman said: “If he runs, it’ll be to ensure the members get an open contest rather than an anointed successor. If we’re trying to build a social movement-style party that can transform Britain, backroom deals are just not the way to go.”
The source said Lansman would be a “unity candidate”. “He’s the only candidate who is both in touch with the membership and able to work with all the different unions that sit on the NEC [national executive committee].”
Corbyn and the shadow chancellor, John McDonnell, have so far supported Jennie Formby, a Unite official, to replace McNicol when his departure is agreed.
If Lansman’s run is confirmed, the battle for the position will expose a faultline which has been quietly growing on the left of the party between Momentum’s desire to see Labour transformed into a member-led movement and the unions’ desire to tighten control on its key offices.
Lansman, a veteran of the Labour left and close friend of Corbyn, is also set to urge the leadership to allow more involvement from members in approving the appointment of the next general secretary, though he is unlikely to suggest the position is elected. Such a change would be likely to require a rule change at the next annual conference.
The general secretary position, one of the most powerful in the party, is decided via an application process to the NEC, which has agreed to a fast-track process which will fill the position by 20 March.

Many in the party believe McNicol’s replacement should be a woman, given men hold most key positions, including those of the leader, deputy leader, shadow chancellor and leaders of its Welsh and Scottish parties.
Applications opened on Tuesday. Formby is the first to have formally announced her candidacy, saying the party was “now united as it has not been for years under Jeremy Corbyn’s leadership”.
In a statement, Formby stressed her experience as a member of the NEC and a senior Unite official in industrial, political and administrative posts.
“I will work with all parts of the movement to ensure that the party democracy review empowers the party membership, opens up policymaking, and ensures democratic best practice throughout,” she said. “I will ensure our exciting new community-organising initiative is developed to help entrench Labour in the communities we serve and win the seats we need at the next general election.”
Formby said she would stand up to antisemitism, racism and abuse in the party and would be proud to be the first woman in a generation to serve as general secretary, the second in Labour history.
“I have fought for gender equality – often the hard way – throughout my lifetime in the labour movement,” she said.
“Labour has only one objective – to bring to Britain the socialist change it desperately needs. And it has only one means of delivering that – electoral victory at all levels, and above all in a general election. As general secretary, I will devote all my time and energy to ensuring that we grasp the historic opportunity before us.”
Others tipped for the position are the GMB political officer Lisa Johnson and Unite’s political director, Anneliese Midgley. Johnson, a potential compromise candidate, has told friends she is happy to remain in her role, but could be persuaded to stand.
A senior NEC source said the support of the GMB union was key to whoever succeeded McNicol. “If GMB decided to back Jennie, she will get it. If they don’t, then it might be a compromise candidate. All of these candidates are experienced and from the left of the party. It would be really good to have a woman in the role.”