On 24 July 2025 a new left-wing party, provisionally named Your Party, was launched by Jeremy Corbyn and Zarah Sultana after the pair unveiled the sign-up site yourparty.uk and reported "hundreds of thousands" of registrations in the first two days [1], [2]. Both MPs sit as independents after losing the Labour whip.

This article outlines the origins of the rift that pre-dates this fragmentation, the parliamentarians who may defect or ally with the new party, and the wider consequences for British politics.

The Background

Jeremy Corbyn’s rise and fall as Labour leader

Jeremy Corbyn’s election as Labour leader in 2015 stunned all those involved in UK politics, whether friend or foe. The sharp shift leftwards had been unexpected. Labour had just suffered a heavy defeat under Ed Miliband, a pragmatic and thoughtful politician that many saw as a bridge builder between the wings of the party. They had lost 26 seats and slipping to 232—its poorest haul since 1987 [3], [4]. Corbyn had scraped onto the leadership ballot with the minimum 35 MP nominations securing just 36 [5]. For more than 30 years he had been a fringe member of the parliamentary Labour party.

Labour’s membership surged for the upcoming leadership election, the party reported 388,000 members by December, almost doubling its pre-election base [6], [7]. Corbyn won the five way leadership contest with almost 60% of the vote. This influx of new members also seeded Momentum, the grass-roots network founded on Labour’s left, founded shortly after he became leader by his supporters.

Corbyn had been expected to fail in short order. Thus it was all the more shocking when in the 2017 election, against Theresa May’s Tory government, he stunned critics again as Labour’s vote share leapt 9.6 points to 40 %. This was its biggest swing since 1945 gaining 30 seats [8]. The achievement was all the more striking because many MPs had branded his EU-referendum campaigning the previous summer “lukewarm” [9]. Although Corbyn had supported the Remain campaign he had made a minimal number of appearances. This had disillusioned many Labour supporters with the vast majority supporting Remain.

Yet, two years later fortunes reversed with a sharp reverse swing: Labour crashed to 202 seats in 2019, its fewest since 1935 [10]. This shocked Corbyn’s supporters whilst emboldening his sceptics. He resigned the Labour leadership shortly afterwards.

Throughout his leadership his shadow cabinet had been made up of loyalists, such as John McDonnell, alongside moderates including Keir Starmer. There had been a clear and welcome attempt to bridge the gap between Corbyn’s fringe wing of the parliamentary Labour party and the centre-left.

However, despite his apparent willingness to compromise those of the far-left crystallised around Momentum which continued to exist following Corbyn’s resignation, albeit seperate from the Labour party, playing a divisionary role on the left of British politics.

Corbyn’s dismissal from the Labour party

The Equalities and Human Rights Commission found Labour in breach of the Equality Act for political interference, inadequate training and harassment in antisemitism cases [11]. Corbyn replied that antisemitism was “abhorrent”, that "one anti-Semite [in the Labour Party] is one too many", but that "the scale of the problem was also dramatically overstated for political reasons by our opponents inside and outside the party, as well as by much of the media."

Keir Starmer called the findings “a day of shame” and suspended his predecessor. Corbyn was later barred permanently. No evidence suggested that Corbyn himself was anti-semitic.

Running as an independent in 2024, Corbyn comfortably held Islington North, cementing the break. Despite rumours of Corbyn rejoining the party Starmer has held fast in his stance that Corbyn could not be readmitted.

Other long-time allies have also been frozen out. Former shadow chancellor John McDonnell was suspended for six months in July 2024 after backing an SNP amendment on the two-child cap and has still not been readmitted [12]. Diane Abbott lost the whip in 2023 over comments minimising antisemitism [13]. Sam Tarry was deselected amid allegations of “vote-rigging” in his constituency party [14], while Beth Winter, a Welsh socialist, was ousted during boundary reselections the same summer [15]. In total, fifteen MPs have been disciplined or removed since 2022—more than in any parliament since the SDP split of 1981 [12].

The history of Corbynism

Jeremy Corbyn has been a an MP since 1982. His political positions have been unwavering in this time generally representing the furtherest left of the parliamentary Labour party. His views were shaped by Tony Benn, his mentor, and his circle of Bennites. Benn was a charismatic character and a self described Christian socialist.

Tony Benn’s political beliefs centred around state planning, strong unions and conviction politics [16]. He was also a known eurosceptic. Many of his positions have been adopted by Corbyn, and remain fundamental pillars of the Momentum movement to this day.

Momentum, the grassroots machine that underpinned Corbyn’s rise, was founded within days of his 2015 leadership victory by organiser Jon Lansman. At its peak it claimed 40,000 paid supporters and ran hundreds of local "Barnstorm" events, explicitly modelling itself on the US Sanders campaign and Occupy tactics [17]. Even after Corbyn announced his resignation, the group vowed to stay and "pull Labour left from below" [18]. Although membership has thinned since 2019, Momentum’s email list and social-media infrastructure have likely become the core mobilisation network behind Your Party with Momentum ceasing to be aligned with the Labour party as of 2020.

Your Party: Who Are They and Who Might Join Them?

Current parliamentary supporters comprise Corbyn, Sultana and the six-strong "Gaza independents" elected in 2024, including Apsana Begum and Claudia Webbe [19]. The platform echoes the Corbyn 2019 manifesto, public ownership of rail and mail, a Green New Deal, wealth taxes over £2 million and an immediate ceasefire in Gaza, while adding proportional representation and a right to strike charter. The latter is in particular a nod to Corbyn’s bennite origins.

Will others follow?

John McDonnell and Diane Abbott — both still suspended — insist the fight to “take back Labour” must continue inside the party [19]. Yet Westminster rumours continue to swirl. Veteran Socialist Campaign-Group MP Jon Trickett is said to be "keeping a close watch" on developments, raising eyebrows among Labour whips [20]. Former shadow cabinet minister Andy McDonald has sidestepped the question when pressed, but allies note his suspension last year has "fundamentally altered" his loyalties [21]. By contrast, Norwich South MP Clive Lewis took to Facebook to declare he is "staying put … now more than ever we need progressive voices inside Labour" [22].

The Green party

Ellie Chowns, Green Party MP for North Herefordshire and leadership contender, dismissed suggestions of working with Your Party ,the party’s parliamentary group flatly rejected any formal electoral pact last week [23]. Overlapping constituencies such as Bristol Central and Sheffield Hallam could become three-way knife-edge fights.

However, Zack Polanski, considered to the left of the Green Party, has said he is open to working with the new party if this served the party's interests [23].

Previous Splits and Possible Consequences

The most eerie parallel is with the 1981 breakaway of the Social Democratic Party from Labour. Within two years the SDP–Liberal Alliance had secured 7.8 m votes but only 23 seats; Labour crashed to 27.6 % of the vote, its worst share since 1935, and the Conservatives governed for 18 more years [24], [25]. Earlier still, splits in the Liberal party during the 1920s handed opposition status to Labour but with the Tories dominating until the end of the decade [26].

Contemporary projections point the same way in first-past-the-post: a party on 10 % evenly spread support wins zero or one seat yet siphons dozens from its ideological neighbours[[27], [28]. In other words though Your Party is unlikely to gain many seats it would substantially diminish the success of Labour, handing victory to the right.

Moreover forecasts suggest that Your Party could break the 10 % threshold. Polling suggests the new party could still attract up to 18 % of voters nation-wide—and a striking 35 % among the 18-to-24 cohort [29]. An MRP simulation by academic co-operatives shows Labour losing 30-plus seats if Your Party fields candidates everywhere, enough to wipe out the 2024 majority.

Lessons for the Left

First-past-the-post, the UK’s electoral system, rewards unified blocs and punishes pluralism. The Electoral Reform Society notes 2024 produced the most disproportionate parliament, compared to the proportion of votes, since the war [30], [31]. Starmer’s calculation, that firm discipline would reassure swing voters, now collides with the fragmentation risk he helped to create. As it stands the Tories or even Reform UK could reap the double dividend of a split left vote. Labour could out-flank Your Party, and attempt to secure an accord with the Green party itself, though history suggests that Starmer struggles with compromise leading to ominous conclusions.

Unity need not require ideological uniformity. Factions of left-wing parties can recognise their common ends, remaining loyal, yet disagree on the means. The lefts willingness to self reflect is a strength, but becomes a weakness when this sows division and loss of trust.

This diversionary mentality is not the sole reserve of the far-left. Starmer’s dismissal of Corbyn played a significant role in the current division. Despite Corbyn’s weak leadership and denial around anti-Semitism it is questionable as to whether permanent dismissal was warranted.

As it stands Labour is unlikely to win the next election with the left so divided and an unwillingness of the left-wing parties to compromise and unite. This should be a warning to the left across our democracies: The process of fracture is often immeasurably difficult to reverse, until it is too late.

References

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[28] T. Guardian, “’Disproportionate’ UK election results boost calls to ditch first past the post,” 2024. Accessed: Jul. 28, 2025. [Online]. Available:https://www.theguardian.com/politics/article/2024/jul/08/disproportionate-uk-election-results-boost-calls-to-ditch-first-past-the-post

[29] YouGov, “Who is open to voting for a new corbyn-led party?” Accessed: Jul. 28, 2025. [Online]. Available:https://yougov.co.uk/politics/articles/52505-who-is-open-to-voting-for-a-new-corbyn-led-party

[30] P. Toynbee, “Even the tories now admit that our electoral system is toxic. When will labour have the guts to fix it?” Accessed: Jul. 28, 2025. [Online]. Available:https://www.theguardian.com/commentisfree/2025/jul/22/britain-electoral-system-tories-labour-first-past-the-post

[31] E. R. Society, “Brexit pacts: The latest desperate attempt to game a broken first-past-the-post system.” Accessed: Jul. 28, 2025. [Online]. Available:https://electoral-reform.org.uk/brexit-pacts-the-latest-desperate-attempt-to-game-a-broken-first-past-the-post-system/