At an early meeting to set the path for what would become Your Party, participants quickly agreed on one thing: given the cliches about leftwingers forever falling out, at all costs they must avoid a descent into factionalism.

Six months on and the Liverpool venue hosting this weekend’s inaugural Your Party conference has been warned to expect potential disruption, including stage invasions by disgruntled members representing particular wings. Extra security guards have been hired.

How did an idea with so much potential traction and reach – hundreds of thousands of people signed up to support the idea of a movement spearheaded by Jeremy Corbyn and Zarah Sultana before it even existed – become so quickly and comprehensively bogged down in power struggles and infighting?

The slightly simplified answer, one agreed on at least in private by people from all sides, is rooted in escalating tensions between Corbyn, portrayed as indecisive and at times ambivalent about yet another political venture at the age of 76, and Sultana, the combative former Labour MP who has enraged colleagues by making major decisions unilaterally.

The ground zero for a split so comprehensive that, insiders say, Sultana has for the past three months mainly communicated with her supposed colleagues through lawyers, came on 3 July, or “terrible Thursday” as one calls it. This was when the Coventry South MP announced she was resigning from Labour and would jointly lead a new entity with Corbyn.

Zarah Sultana addresses the crowd at a Stop Trump Coalition protest in Parliament Square in September. Photograph: James Manning/PA

The news followed a meeting of the embryonic organisation earlier that day at which the co-leadership was discussed. There was, however, one problem: Corbyn and his allies firmly believed that no decision was made.

Their surprise at Sultana’s fait accompli was briefed to the media, while an internal WhatsApp group descended into intense disagreement. It took until the next afternoon for Corbyn to respond publicly, with a tweet pointedly saying that discussions were “ongoing”.

It highlights the contrasting and often incompatible personalities of the party’s protagonists, one where Sultana either believed Corbyn’s lack of a firm answer on co-leadership was a tacit yes or simply chose to bounce him into it.

Even allies of Corbyn say the former Labour leader can be hard to pin down, with an aversion to open conflict and a tendency to, as one person involved in the project put it, “disappear to his allotment for 24 hours without his phone”.

“Jeremy can be a touch avoidant,” one ally said. Another source involved in the project was more blunt: “That’s always been the problem – he won’t say anything. You have this whole industry of Jeremy-whisperers, trying to interpret what he means.”

A source close to Corbyn disputed the idea he was wary about leading the party and said it was for members to decide. The idea he disappeared to his allotment was, they added, “complete nonsense”.

Corbyn said: “Lots of people have said a lot of things about me. I will carry on representing my community in parliament and speaking out against inequality, poverty and war.”

The first push for Corbyn to lead a new leftwing party came before last year’s general election, at which he stood in his Islington North seat as an independent. These overtures were rebuffed. There are some who view him as still slightly reluctant, but urged on by Karie Murphy, his chief of staff when he was Labour leader, and his wife, Laura Alvarez.

After the election, Corbyn suddenly found himself one of five left-leaning independents, with Shockat Adam, Adnan Hussain, Ayoub Khan and Iqbal Mohamed winning urban, formerly Labour seats on Gaza-focused platforms. Two months later they jointly formed the Independent Alliance.

Adnan Hussain, the MP for Blackburn, was one of five independents to form a parliamentary alliance with Corbyn after the election. Photograph: Imageplotter/Alamy

By this point, discussions had begun about the possibility of launching a new Corbyn-focused, not necessarily Corbyn-led, political movement.

While a platform of specific policies will have to await agreement on a leader or leaders, those involved in Your Party argue they will have a voice distinct not just from Labour but also the Greens, with a focus on community organising, internationalism, nationalisation and redistribution.

But from the start, there were difficulties. “The first meeting was very disorganised,” one source recalled. “It started late as they were waiting for Jeremy to turn up and then the agenda kept changing.”

The coming months produced progress, including an outline of the party’s philosophy, but also disagreements: for example, attempts to create a powerful role of general secretary, viewed as a means for Murphy to take over.

Into this slightly ponderous mix arrived Sultana, whose punchy social media presence reflects an MP keen to get things done, but one with a tendency to fall out with people who could be allies.

“Zarah has made her profile by being combative and there’s clearly a place for that,” said one observer. “But her diplomacy has been shockingly bad. There has been a complete failure to either produce an alternative plan, or win people over.”

An ally of Sultana said she sought to work collaboratively but was excluded from decision making process, and that she remained fully focused on the party and its mission.

If the divide created on 3 July was bad, worse was to come when Sultana unilaterally launched a membership portal, collecting reams of data and about £800,000 in donations and levies.

Your Party had spent £13,000 on a software system intended for this process and Sultana planned to use it for her membership drive, the Guardian has been told. But she was thwarted when Corbyn’s allies learned of her plans and sent a staffer into the organisation’s offices at 3am to change the passwords, sources claimed.

Sultana pressed on, using her own software, prompting fury from Corbyn. He accused Sultana of creating a “false membership system” that had collected money and data without authorisation, and said Your Party had referred Sultana to the Information Commissioner’s Office. In response, Sultana said she was consulting defamation lawyers over what she called baseless claims from a “sexist boys’ club”.

Since then, the tensions have become less dramatic, if no less entrenched. Much of the recent disagreement has centred on how the money can be passed from a holding company set up before Your Party existed to the party itself, with counterclaims of delay and of a failure to understand the basics of company law.

Possibly more damaging was the departure of two of the independent MPs, Hussain and Mohamed. The former lashed out at what he called “persistent infighting” and a “toxic, exclusionary and deeply disheartening” culture, rancour based in part on issues such as transgender rights.

For now, Adam and Khan remain in place, but the departures highlight the difficulties in creating a party encompassing Sultana and Corbyn, along with the often more socially conservative electoral bases of the other independents.

Jeremy Corbyn and Zarah Sultana on a picket line outside London Euston railway station in July. Photograph: Stefan Rousseau/PA

“At one point we had six MPs and four different factions,” one source said. Another observer blamed what they called “bridge burning” by Sultana. “This is not to say that independent MPs are flawless, but if you’re going to build a big thing you need to work with a lot of people.”

As members travel to Liverpool to decide on everything from a leadership structure to a name – Your Party was only ever an interim choice – opinions differ on what might come next.

“I think it’s toast,” one participant said, noting how the splits in Your Party have been mirrored by a surge in membership and attention for the Greens under their new leader, Zack Polanski.

Some omens remain unpromising. Sultana’s decision to hold a self-organised pre-conference rally in Liverpool on Friday evening, billed an official Your Party event, annoyed others in the party.

And although Your Party members are barred from also being members of other parties, Sultana is backed by the Socialist Unity Platform, a lobby organisation comprising groups including the Communist party of Great Britain. It is from here that possible disruption is predicted.

Others see the conference as a chance to move forwards, especially if members choose the option of collective rather than individual leadership, thus preventing a long and possibly brutal contest between Corbyn and Sultana.

“One reason for going so soon to a conference is because we can’t decide anything among ourselves, so it has to go to the membership,” one insider said. “Then, maybe, a committee can move forward like normal human beings.”

Despite the drama, there is seemingly an appetite for a leftwing challenger to Labour that is not the Greens, shown by the mass sign-ups and by about 3,000 people heading to Liverpool for an event only weeks in the planning.

“This is a long-term project,” said one person who is, at least for now, involved in it. “Who knows where we will be in a couple of years? There are likely to be areas of the country the Greens can’t get into, and we could cooperate.

“By then we might be saying: ‘Do you remember that absolutely mental period at the start?’ But this conference has to provide some stability and some structure. It doesn’t need to be perfect, but it does need that.”