Freedom of movement, one of the EU’s key pillars, is precarious as the UK heads for Brexit. Thousands of Labour activists are in favour of protecting the principle, and are calling on their party to defend migrants’ rights.

A group gathered at Labour party conference to call on the leadership to protect the rights of migrants. At an event entitled “What Should Labour’s Migration Policy Be?”, held by The World Transformed (Momentum’s alternative politics festival), activists from the left of the party working on the Labour Campaign for Free Movement criticised the party’s reticence on the subject.

They expressed disappointment that party members had voted not to debate the details of Labour’s Brexit policy, including free movement, at this conference (a move engineered by Momentum).

“My impression of this conference has reinforced in my head the awful process that’s going on inside the Labour movement in terms of free movement and migrants’ rights,” said Michael Chessum, a Labour Campaign for Free Movement organiser who represents the left-wing Another Europe is Possible group, and used to be on Momentum’s steering committee.

He told the event that there is a section of the left aspiring to “older, Stalinist politics whose arguments about immigration being wrong, borders being great, used to be on the absolute periphery on the left”, finding their “straight-up, right-wing nationalist arguments” have “all of a sudden become mainstream on the left” after Brexit.

Chessum also blasted a “large section of the left who do believe in free movement, who are instinctively in favour of it, becoming massive wimps. We’ve just ducked a debate on Brexit because we’re scared.”

This was a reference to party members voting to debate other issues than Brexit on the party’s conference floor this autumn – a decision that was announced this morning.

Chessum tells me he believes Jeremy Corbyn is in favour of migrants’ rights but, as they have been tied up with the question of whether Labour would advocate permanently staying in the single market, he is avoiding the subject. “We cannot wait for white smoke to appear from the Leader's Office,” Chessum adds.

The question of free movement represents two growing divides in a Labour party at its most united since the summer of 2015.

Firstly, the most vocal activists in favour of free movement are on the party’s left but they find themselves at odds with – or at least frustrated by – the Leader’s Office and Momentum, with the former being reticent on the issue, and the latter not having a line on it (as with other policy). For example, Chessum criticises what he sees as an “opaque” decision-making process that led Momentum to rally its members to request motions other than Brexit to vote on at conference.

“Jeremy is now safe,” he tells me. “We are no longer under constant siege and constant threat of another leadership election. We’ve won the internal debate about having a left-wing leadership, and we can afford to have a debate about these issues.”

Secondly, they don’t want to be associated with voices to their right arguing for single market membership, such as Alison McGovern MP, who chairs the Blairite Progress group. They believe free movement being conflated with the politically contentious issue of single market membership hinders their cause.

“I don’t want to go into a room lined up with people who are from the centre of the party,” says Chessum. “I want to have a debate about free movement specifically.”

This is where many of Labour’s Corbynite members stand. Michael Walker, from the alternative left news platform Novara Media, told me in August that he and his colleagues will be covering freedom of movement “because that’s one of the contentious issues on the Labour left and the Labour party’s new members – less about the single market.

“We don’t, our audience doesn’t really care – I mean, I don’t really care about the single market. We talk more about migrant rights than we do about trade.”

The free movement issue provides an opportunity for Corbyn, therefore, to please many of his members without having to support membership of a single market he’s never been keen on. But his recent comments on migration from the EU suggest it’s not one he’s yet prepared to take.