Simon Fletcher, Jeremy Corbyn’s director of campaigns, has quit the leader’s office.

Fletcher was Corbyn’s campaign manager in his first bid for the Labour leadership, and his chief of staff until 3 June 2016, when he was appointed director of campaigns and tasked with getting the party fighting fit for the election.

This resignation was a long time coming. Some saw Fletcher as a crucial lynchpin of the office, who held things together “through force of will” in the words of one insider. In the early days of Corbyn’s leadership, he operated as chief of staff, press officer, head of rebuttal, chief strategist and speechwriter while the work of hiring a team around Corbyn went on. However, that meant others saw him as responsible for the missteps of the early days.

He and Seumas Milne, Corbyn’s communications chief, were often at odds. Fletcher and Anneliese Midgley, his deputy, both refused to take part in a Vice News documentary about Corbyn which was widely panned and presented an unflattering view of the leader’s office.

But in a signal of where power in the leader’s office lay, Midgley quit in April to take up a post as political director at Unite.

Shortly thereafter, there was an internal reshuffle of the leader’s office, with the abolition of the role of chief of staff and the introduction of a new “flat” structure. Fletcher became director of campaigns and planning, Milne became director of communications and strategy, Andrew Fisher was director of policy and Karie Murphy was director of the leader’s office, responsible for running the leader’s office day-to-day.

In a further confirmation of Milne’s internal success, he made his loan move from the Guardian permanent at the turn of the year, while Murphy has an enhanced role running the leader’s office day to day. In addition, new hires in the communications department - James Schneider and Matt Zarb-Cousin - both came with the Milne seal of approval, in contrast to his previous deputy, Kevin Slocombe, who was a Fletcher hire.

Opinions of Murphy differ wildly. In the leader's office, she is seen having brought significantly improved organisation and greater intensity to the team. But what call an insistence on high standards, others see very differently.

Friends of Jon Trickett say that she was instrumental in pushing him out as the party’s election coordinator. The two clashed at one recent meeting and allies of Trickett, now demoted to the Cabinet Office, say that she made his job “unworkable”.

Insiders say that Murphy is “waging war” on multiple members of the leader’s office, with one dubbing her a “control freak”, who was keen to add Fletcher’s role of oversight for the election campaign into her own orbit.

“The thing about Jeremy,” says one senior source, “Is that he can tell people what they want to hear, and then he has to get Seumas or Karie to tell them what he really wanted to say. So you’ll read stories about how Seumas has forced something through or Karie has gone over Jeremy’s head, but actually that’s not it at all.”

But for critics of Murphy's, Fletcher’s exit, they say, will exacerbate the low morale and internal tension in the leader's office.

Whoever is right about what comes next, the central truth remains: Fletcher’s resignation is a sign of internal victory for Milne and Murphy.