Leftwing Labour MPs have expressed private fears that they could also lose the Labour whip after Keir Starmer’s decision to bar Jeremy Corbyn from standing for the party. The move has also put into question the future of the campaign group Momentum after Starmer said those who did not back his leadership should leave the party. Activists at the grassroots group said they were determined to remain a Labour campaign group and support Labour candidates. Momentum said it had had its biggest surge in new members for many months and said it would in future be putting pressure on policy issues such as nationalisation and wealth taxes. The determination of the group to remain influential within Labour is a strong hint it would not campaign for Corbyn as an independent candidate – though no final decision is likely to be taken until Corbyn himself takes one. The party is likely to suspend any members if they support Corbyn against a Labour candidate, though the former leader has said his initial intention is to exhaust all routes to run for Labour. Momentum’s Hilary Schan said, in response to Starmer’s invitation for critics to leave the party, that “the door might be open – but we’re not leaving” and said the group was still calling for people to rejoin Labour. But leftwing MPs have described feeling like they are being closely watched for transgressions, with one describing it as having to “watch for traps being laid for us, second-guessing whether we’re being set up”. Only two MPs have spoken out about Corbyn’s suspension – the Labour MP Diane Abbott and the now independent MP Claudia Webbe, who had been a close supporter of Corbyn but was suspended after a court case. Allies of Starmer now hold all the main levers of power in the party and say the strategy of rejecting the mistakes of the Corbyn years, especially being tough on antisemitism, is reaping major rewards in the polls, where Labour is 20 points ahead. But among the Socialist Campaign Group of MPs, many alleged the party was no longer able be the broad church that it was under other successful Labour leaders such as Clement Attlee and Harold Wilson, or even under Tony Blair. “It’s unprecedented in Labour history,” said one MP, pointing to a tweet by the shadow Northern Ireland secretary, Peter Kyle, that said: “If you’re antisemitic or you don’t agree with support for business … then this isn’t the party for you.” The MP said that, by implication, it suggested differing views on the economy were not welcome – and that was on a par with being an antisemite. They said it was not a climate conducive to attracting activists. “These are people who want to be prime minister, being a member is meant to be inspiring and enjoyable but people feel they are being constantly monitored.” There are some around the Labour leader who still believe Starmer should eventually force out more Corbyn-associated MPs, especially any who had been equivocal on the seriousness of Labour’s antisemitism problem or on support for Ukraine. “I still think we should have suspended more of them over Stop the War, but Keir gave them another chance,” one senior Labour source said. “Now all of the SCG are being extremely careful.” Momentum has refocused much of its campaigning efforts on policy in recent months, having previously devoted a lot more energy on influencing constituency selections to elect more leftwing MPs. But that has been thwarted repeatedly by the tight hold that the national executive committee has kept on local selections. Schan said it was clear Momentum’s leadership still very much wanted to remain closely associated with Labour and campaign for change within the party. “What we stand for is a set of policies, a set of views that Keir Starmer seems to be deeming illegitimate,” Schan said. “We’re not going to be pushed out just because one man has decided that he doesn’t like us.” Momentum’s resources have gone into campaigning on key issues such as fair wages for public sector workers – criticising Starmer for his picket line ban on MPs – as well as calling for further nationalisation and speaking out against further private interests in the NHS. The group has had some new victories in grassroots Labour bodies including Young Labour and Labour Students on a platform of abolishing tuition fees. But funds are also tight for the organisation, which had to launch a major fundraising drive last year. “We are pulling every lever that we can for socialist policies,” Schan said. “When you look back at the popular policies that Labour has actually announced over the last few months, they’ve all been drawn from the left, whether that’s public ownership of rail, a huge rollout of council housing or the windfall tax.” Momentum said it was lining up a new blitz of campaigning in the next few weeks, including around Labour’s National Policy Forum consultation, the last before the next manifesto, working in tandem with the SCG. There will also be a new grassroots organising push, with events across the country as well as starting its local election campaigns.