Momentum's website gives an account of how the organisation was born out of the 2015 leadership campaign that saw Corbyn triumph over three leadership rivals with 59% of the vote in the first round of balloting.

The movement, it says, is "the successor to the campaign to elect Jeremy Corbyn as leader of the Labour Party" and is aimed at making Labour more "open" and "member-led" – as well as winning elections – through "inclusive events, rallies, meet ups and policy consultations".

Official records seen by BuzzFeed News show the company that became Momentum Campaigns Limited was founded as Jeremy Corbyn Campaign 2015 (Supporters) Ltd on 24 June 2015 by Jon Lansman, then parliamentary researcher to the now-deceased Michael Meacher MP, a staunch Labour left-winger.

The company, which had Lansman as sole director, was established to "control and process information collected in the course of Jeremy Corbyn's Labour Party leadership campaign", according to its articles of association. This meant it received the formidable database of email subscribers to and supporters of Corbyn's summer 2015 campaign for leadership.

Lansman became a controversial figure through the leadership campaign after tweeting spoof posters suggesting that Liz Kendall, then a rival leadership candidate, was standing for the leadership of the Conservative party.

BuzzFeed News understands from people present first in Corbyn's campaign and then Momentum that this and other issues led to tensions between Lansman and other leaders, leading to struggles over who would have control as Momentum was established.

On 8 October, James Schneider – now Momentum's national organiser – issued a press release announcing the group's launch as a "grassroots network arising out of, and following, the Jeremy Corbyn for Labour Leader campaign".

Just over two weeks later, official records show, Lansman changed the name of Jeremy Corbyn Campaign 2015 (Supporters) Ltd to Momentum Campaign Limited.

After the company was renamed again this week – without any apparent discussion among Momentum's dozens of local groups or members – as Jeremy for Labour Limited, Schneider replied to a Twitter question from a former Labour staffer about the move saying "that company isn't Momentum".

Schneider then tweeted that "Momentum is an unincorporated association", a different type of legal structure often used by political and campaigning bodies. He also told another user that another, separate company set up by Lansman on the same day "has nothing to do with Momentum".

What Momentum Campaign Limited did