Len McCluskey once joked that Labour MPs were so paranoid about the closeness of Unite and Momentum, they were worried about “a secret tunnel linking Unite HQ to Jon Lansman’s home”.
However, a battle to be Labour’s new general secretary is set to expose a faultline which has been quietly widening on the left of the party – between Momentum’s desire to see Labour transformed into a member-led movement and trade union interests in keeping tight control on its key offices.
The departure of Labour’s general secretary, Iain McNicol, lit the touchpaper this week. Lansman, the founder of Momentum, is taking advice about the possibility of challenging Unite’s chosen candidate, Jennie Formby, who has the support of the leaders’ office.
Historically, Momentum has been close to Unite and leftwing trade unions, setting up its first offices in the headquarters of the TSSA union. However, senior figures in Momentum now believe the group has a big enough support base to begin challenging party orthodoxy on its own terms, even if it means going head to head with trade unions. One described it as a “healthy tension” which was necessary to balance the powers within the party.
Since its creation, Momentum has acted as both the muscle and the mouth of Corbyn’s vision to transform the party into a member-led social movement, but it now has sufficient power of its own to begin influencing the direction of the party beyond unquestioning support.
Momentum has its own offices in east London, more than 30,000 members, and is financially independent, with 90% of its donations coming from membership fees and individual donations, not unions. Senior Momentum figures have wondered for a while whether the group needed to show its independence, and when would be the right time.
“Our agenda is transforming the party. There are going to be places where Momentum and the unions disagree,” one source said. “What we want to make sure, first and foremost, is that the party is run collectively.”
Momentum has never before felt the need to show its strength to the leaders’ office before, but Lansman was reportedly infuriated by the decision to appoint McNicol’s successor in a fast-track timetable of just three weeks and on the assumption that Formby would be the left’s candidate.
Lansman’s decision to run would put him firmly at odds not just with Unite, but with the leaders’ office. Close allies of Corbyn are known to back Formby; these include one of his closest aides, Karie Murphy, and the shadow chancellor, John McDonnell. The Corbynite blog Skwawkbox and the MP Chris Williamson publicly backed Formby, the union’s former political director and a seven-year NEC member, shortly after she announced her decision, on Tuesday lunchtime, to run. A raft of other MPs followed shortly after.
Many in the party believe McNicol’s replacement should be a woman, given that men hold most key positions – that of leader, deputy leader, shadow chancellor, heads of the Welsh and Scottish parties, and all of its metropolitan mayors.
Others in the running for the position of general secretary are the GMB political officer Lisa Johnson and Unite’s political director, Anneliese Midgley, who has tweeted her support for Formby.
The position is decided by a vote of the party’s full national executive committee. Key to the decision will be Corbyn-sceptic members of the committee, as well as the other larger unions Unison and GMB, which have not backed Formby so far.
Union officers on the party’s ruling NEC do not speak as one voice, with Unison and Unite regularly at odds, but none wants to see their bloc’s influence diminished.

One source on the NEC’s moderate wing said they had observed the tension between Momentum and trade unions for a while. “This could well be the moment the whole thing blows,” the source said. “The unions really should have seen this coming – everyone can see it apart from them. The reality is, there is not just one ‘project’ for the future of the Labour party, there are many projects, and sometimes they coalesce around mutual interests. And sometimes they don’t align at all.”
Corbyn recently drafted in McCluskey’s chief of staff, Andrew Murray, a former communist party member, as a part-time consultant to his office, and Murphy is also closely associated with Unite. The union gave Labour £4.4m at the last general election.
“Lots of people are worried about Unite influence in the leaders’ office and controlling the general secretary,” another Momentum source said.
Should Lansman stand, it would likely be a personal wrench for Corbyn, who has been a longtime close friend of the Momentum founder since he worked on the 1981 deputy leadership campaign of Tony Benn, Corbyn’s political idol.
Tensions have simmered since the compromise reached at last year’s conference to give new seats on the NEC to members, after hard lobbying by Momentum. However, unions also secured an extra seat on the ruling body as a compromise to ensure that their influence was not diminished.
“It was very clear then that the union-controlled NEC wants democratisation of the party as long as it suits them,” a source said. “It was democratisation from the top down – it should come from the bottom up.”
So far, key figures in Momentum have shown no desire to flex their muscles on policy, especially not on Brexit, despite large numbers of their members being firmly pro-EU.
There are other issues, though, that could throw open future divisions with the unions. Momentum’s members are far more likely to back nuclear disarmament, oppose the expansion of Heathrow or be sceptical about nuclear power, all areas where Corbyn is sympathetic. Unions, however, especially Unite, cautiously back those policies, for the most part because their members are employed at airports and on nuclear submarines.
But Lansman made it clear, in a previous interview, that he believes in the wisdom of the membership on key policy issues too. Members, he has argued, opposed the Iraq war, opposed PFI and opposed austerity, even when those were all part of Labour policy – and had been proved right.