Momentum’s future is at risk from serious financial challenges, the group will warn its supporters this week, amid an exodus of leftwing members from Labour. The grassroots group, which emerged from Jeremy Corbyn’s 2015 leadership campaign, has launched a fundraiser with a plea to supporters, titled “Keep Up Momentum”. In a video posted on social media alongside the campaign, the group says: “We can’t let everything we’ve built disappear.” The group chiefly relies on individual donations, but also requires supporters to be members of Labour – which has had a knock-on effect on its funding, as thousands of leftwingers have deserted the Labour party under Keir Starmer’s leadership. Insiders say Momentum’s financial situation is “serious, but not critical” – affected by the impact of inflation and reduced income through member subscriptions. The Guardian understands Momentum’s membership is down by a third from its peak during the Corbyn years. One Momentum source said the group wouldn’t “be able to continue to operate at the level we have been” unless more donations were found. The fundraiser has been backed by a number of leftwing Labour MPs from the Socialist Campaign Group, including John McDonnell and Ian Lavery, as well as members of the 2019 intake such as Nadia Whittome, Zarah Sultana, Bell Ribeiro-Addy and Apsana Begum. But there are also many within the group that believe it needs a fundamental change in strategy, including a greater focus on policy battles that the group can influence. Momentum’s co-chair, Hilary Schan, said it was a difficult time for the left in the Labour party, amid controversy over party selections where leftwing candidates have been excluded from shortlists. Starmer also now has significant control over the party’s internal machinery, including a majority on the governing national executive committee. Schan said leftwing members had seen “reams of unjustified suspensions over the last couple of years and more recently the stitch-ups with the selections taking away local members’ voices”. Another senior Momentum source said there had to be a change of approach from the grassroots group. “It’s time for Momentum and the wider Labour left to put forward a coherent plan with a strategy,” the source said – saying that the group no longer has a strong base in the party and had to find a purpose regardless of Corbyn’s future. James Schneider, Corbyn’s former adviser and the group’s co-founder, said Momentum was “stuck fighting its corner in the Labour party” and said it needed to direct resources towards leftwing causes in the country. “Right now there’s a progressive energy in the country, it’s very much in movements, labour movements, environmental movements, anti-racist movements, etc, and Momentum is a bit insulated from that.” A senior Labour source dismissed the possible collapse of Momentum, but said it had an “obsession with damaging the Labour party” and was out of touch with the modern party. “Let’s be frank: they are utterly irrelevant.” Schan said the group had to survive in order to be able to influence the policies of a future Starmer government. “We’re not in the 1990s,” she said. “The situation that a Labour government will inherit will be very, very different from the situation that Blair inherited in the 90s. So Starmer’s tepid, managerial-style policies are just not going to cut it. We need to be there with the real solutions that will change people’s lives.”