The shadow cabinet consists of 36 Labour MPs who hold specific policy briefs and senior roles in the party. They are the most senior Labour figures and are well-known for representing Jeremy Corbyn in public and in parliament. While his initial shadow cabinets were a mix of moderate figures and true Corbynites, nearly all members are fully loyal to the leader as his grip on the party has grown.

A small number of influential academics and think-tank members who formulate the basis of Mr Corbyn’s economic and social policy agenda.

The party’s ruling body. The National Executive Committee decides Labour’s policies and overall direction. It includes members of the shadow cabinet, MPs, representatives of constituency Labour parties, MEPs, activists and trade unionists. Traditionally a thorn in the side of party leaders, Mr Corbyn has gradually taken control of the NEC. In the last round of elected positions, all the positions were filled by candidates running on a Corbynite platform.

A non-party-affiliated movement launched in 2013 holding mass rallies against the Conservative government’s cuts to public spending. The rallies sowed the seeds for the rise of Corbynism two years later.

Traditionally the most hard-left caucus of the Parliamentary Labour party, its origins lie in Tony Benn’s controversial decision to run for the deputy leadership and it proved crucial in Mr Corbyn’s leadership bid.

An amorphous group of centre-left Labour MPs who set themselves against the New Labour project - while eschewing “hard left” politics. Ed Miliband’s leadership was a high point for the soft left’s control.

The leader of the opposition’s office - known informally as Loto - is the main source of power in the party. The most core Corbynites either work in or next to Mr Corbyn’s office in the Norman Shaw South building within the Palace of Westminster. Loto has often been at war with the Parliamentary Labour party and Labour HQ, but its decisions are rarely challenged.

Formed in 2004, the LRC was inspired by an earlier group with the same name, founded in 1900 to “secure representation in parliament for organised labour”. Chaired by shadow chancellor John McDonnell, the LRC includes many of his key allies.

Some traditional Labour socialists — including Mr Corbyn — are longtime sceptics of the EU, decrying the bloc as a capitalist club that favours banking cartels over ordinary workers. Others have more pragmatic reasons for leaving the bloc, for example to shore up their working class vote.

Grassroots organisation formed after Mr Corbyn became leader in 2015, blamed for harassing MPs and changing constituency parties.

Activists, councillors and MPs based in Islington, London

Founded in 1973 to ensure Labour MPs followed the will of Labour’s activists and annual conferences, forcing rule changes on mandatory reselection, for example.

Like all politicians Mr Corbyn has supporters in the media. But more so than past leaders, he has a band of devoted commentators who pen columns, debate on rolling news channels and argue on Twitter to further his cause. Although these cheerleaders deny any coordination with the leader’s office, they tend to fervently defend Corbyn and only criticise him lightly.

Launched in September 2001, just days after the 9/11 terror attacks, as an advocacy group against western foreign policy and the US’s “war on terror”.

Pro-environmental, leftwing party that shares many of Mr Corbyn’s views on economics, foreign policy and domestic policy. It has one MP, Caroline Lucas, but returned seven MEPs in the 2019 European Parliament elections.

The country’s most important local government body, responsible for running the capital between 1965 and 1986 and led notably by Ken Livingstone with Mr McDonnell as deputy until he was sacked for being too radical.

Both a leftwing magazine and a semi-secret pro-Soviet faction within the Communist Party of Great Britain in the late 70s.

The colloquial name given to followers of Tony Benn, the prominent Labour leftwing minister, MP and campaigner. After serving in Harold Wilson’s governments of the 1960s and 1970s, Benn moved dramatically to the left and advocated radical policies for re-nationalisation and boosting the state’s role. He founded the Socialist Campaign Group to further his ideas. Notable Bennites included Mr Corbyn and Jon Lansman.

A leftwing anarchist movement established in 1982, Class War began as a newspaper and briefly morphed into a political movement.

Dating back to 1920 it has only ever returned four MPs; the last in 1950. Following Mr Corbyn’s rise to leader, the Communist Party of Great Britain urged its followers to back Labour instead.

The party’s headquarters in the Southside office building in Victoria Street in London was seen by Mr Corbyn’s inner circle as a nest of opposition to his project (it was once labelled “Darkside”). Responsible for membership, discipline, media queries and general administration, Southside is now run by senior Corbynites and is loyal to the party leader.