Jeremy Corbyn has moved to dispel rumours he is considering standing down as Labour leader, insisting that “of course” he will serve a full term as prime minister if the party wins the coming general election.

The Labour leader was speaking amid a chaotic start to the party’s annual conference in Brighton, with the resignation of a senior aide and a failed bid to oust his deputy Tom Watson.

Head of policy Andrew Fisher, who wrote Labour’s 2017 election manifesto, walked out with a memo – obtained by the Sunday Times – in which he said he no longer believed the party would win power and denounced Corbyn’s team for “lack of professionalism, competence and human decency” and said he was sick of their “blizzard of lies and excuses”.

Speaking on BBC1’s Andrew Marr Show, Mr Corbyn confirmed he had seen the memo but insisted he still enjoyed a “convivial” relationship with his aide, who he said was leaving at the end of the year in order to spend more time with his family and get away from a “very stressful and very full-on job”.

He suggested Mr Fisher’s comments were the result of a momentary anger: “I think he said that because he was extremely distressed at that point about whatever was going on in discussions in the office at that moment. I would have thought that similar memos fly around the BBC every day.”

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Corbyn overruled a bid to remove Watson by abolishing the deputy leader’s position, but Labour’s ruling National Executive Committee agreed new rules allowing the left-dominated body to appoint an interim successor if the leader resigns or is incapacitated, rather than the deputy automatically taking over.

The manoeuvring over Mr Watson’s position has sparked speculation that factions within Labour are preparing for a handover of power by 70-year-old Mr Corbyn, amid claims that he is tiring of the job.

But asked whether he was considering retirement, Mr Corbyn dismissed the suggestion as “wishful thinking by some people” and insisted he was “enjoying” the work.

Andrew Fisher

“I’m taking the party into the general election,” he said.

Challenged over whether he would serve a full five-year term as prime minister, which would see him in Downing Street until he hits 75 in 2024, he replied: “Of course, why wouldn’t I? I’m very surprised at this question.”

Mr Corbyn said he was not aware that a motion to abolish the deputy leader's office was set to be tabled at Friday's eve-of-conference meeting of the NEC and was not present for the vote, which failed after opponents of Watson led by Momentum chief Jon Lansman failed to secure the two-thirds majority needed to overturn the chair's ruling that it was out of order.

"I'm not all-seeing and all-knowing," he said. "I would love to be."

At a follow-up meeting of Labour's ruling body on Saturday, the NEC approved a motion from Corbyn for a review of leadership structures, with a view to creating two deputies, one male and one female.

The Labour leader described Mr Watson's description of Friday's meeting as a "drive-by shooting" as "strange language".