Jon Lansman, the founder of Momentum, the grassroots organisation set up in 2015 to support the left wing of the Labour party under the leadership of Jeremy Corbyn, has announced he will step down from his role as chair of the group. Writing on the Labour List website, Lansman – who will remain a member of Labour’s national executive committee (NEC) – declared it was time for a new generation of leaders to campaign for socialist policies and to put their ideas into practice, as he revealed he would not stand in internal Momentum elections in June. The veteran political activist called for better governance within Labour, and demanded “justice for sabotage” and for the alleged misuse of funds, as well as for “racist, sexist, ableist and frankly McCarthyite attitudes” that he claimed the leaked report into the party documented. “We are now a mass of dedicated activists fighting for a better world,” he wrote. “And in this new era, it is time that a new generation of leaders put their ideas into practice. That is why I have decided not to contest the forthcoming elections within Momentum and instead will hand over to a new leadership.” He continued: “We desperately need better governance in our party, as the leaked report has further demonstrated. Members need justice for sabotage, misuse of funds, plus racist, sexist, ableist and frankly McCarthyite attitudes. “But we must also make sure that the party’s machinery never again returns to those days of anti-democratic stitch-ups, factional warfare, and toxic culture.” The longtime campaigner, who studied economics at Cambridge in the 1970s, notably worked on Corbyn’s campaign for the party leadership in 2015 which culminated in the unlikely return of a socialist to the role. He wrote that upon Corbyn becoming leader, socialists were few in the Labour party, but “today we are many” and there was “real cause amongst us for hope and confidence”. Lansman added: “In 2017, with an incredibly popular socialist manifesto, we achieved the biggest swing to Labour since 1945. Promising to restore public ownership and end austerity, we came within just 2,500 votes across a handful of constituencies from forming a government.” He credited the movement around Corbyn, bolstered by Momentum’s grassroots campaigning and viral videos, for forcing Labour to “never again be the party of illegal invasions, anti-immigration mugs or support for Tory policies of austerity and privatisation”. However, he lamented that the NEC was unfit for purpose and said it needed to be given greater powers to provide adequate scrutiny and oversight over the party and its leadership. It comes after he was campaign chief of Rebecca Long-Bailey’s unsuccessful run for leadership, in which she lost out to Keir Starmer. Long-Bailey tweeted Lansman her best wishes, describing him as a “tireless voice for Labour party democracy”. Angela Rayner, the party’s deputy leader, also tweeted to wish Lansman all the best, calling him “a true socialist” who “has fought injustice and inequality and will continue to do so”. Of the attempts – sometimes controversial – to reselect parliamentary candidates in certain constituencies by leftwing activists, Lansman wrote: “We didn’t succeed in democratising the party sufficiently while Jeremy was leader, but we must not give up now. It’s now more important than ever that Labour becomes a grassroots member-led movement.” Acknowledging he had made mistakes and had some regrets – without revealing what they were – Lansman said the struggle for an equal and environmentally sustainable world would continue, though there has been speculation about whether Momentum can survive Corbyn’s departure. “I shall stay around to support my successors in Momentum,” he said. “I shall continue to speak out, even when some would rather I didn’t.” He added that he would return to blogging and focus his attentions on Labour’s national executive committee. A spokesperson for Momentum thanked Lansman for his years of dedication to the Labour party, saying: “He has done an incredible amount to transform the politics of this country. He has played a key role in building Labour into a half-a-million-member party and strengthening the movement for socialism in Britain. “We look forward to working with him as he continues to lead from the left on the NEC and across the movement.” The Forward Momentum campaign, which set out last month to “refound” and “democratise” Momentum, said it was pleased Lansman had recognised it was time for a new generation to take the organisation forward. “We need to put an end to stitch-ups, and candidates or slates being chosen behind closed doors in London,” it said in a statement. “We need Momentum to be a truly member-led organisation that campaigns to transform the Labour party and supports trade unions and social movements in their struggles for social and economic justice.”