On Thursday the party narrowly won the Batley and Spen by-election by 323 votes. There had been speculation Sir Keir would have faced a leadership challenge if Labour lost the seat.

       Instead he could now seek to strengthen his position, by changing the system for election Labour leaders.

       According to the Daily Mail Corbynites fear Sir Keir will dump the “one person, one vote” system which let Jeremy Corbyn win in 2015.

       Instead he could revert to a system that divides votes evenly between Labour MPs, members and affiliated trade unions.

       Next month Unite, one of Britain’s most influential trade unions, elects its next general secretary.

       It had been led by Len McCluskey, a fierce ally of Mr Corbyn.

       However if moderate Gerard Coyne takes the crown, defeating leftist Steve Turner, Sir Keir could be emboldened.

       Speaking to the Mail one left-wing Labour MP said: “If that happens, we all expect Keir to try to ram this change through conference this autumn.

       “It doesn’t make it impossible for a Corbyn Mark Two to win the party leadership again, but it would make it very, very difficult.”

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       In September 2015 Mr Corbyn shocked the political world, by winning Labour’s leadership election with 59.5 percent of the vote.

       A new “one member, one vote” electoral system had been introduced, reducing the influence of MPs and trade union leaders.

       Labour supporters were also able to vote if they became affiliate members, costing just one pound, even if they didn’t become full members.

       In 2019 Mr Corbyn led Labour to its worst general election defeat since 1935, winning just 202 seats to the Tories 365.

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       Speaking to Sky News Rachel Reeves, the shadow chancellor, praised Sir Keir’s leadership.

       She said: “Under Keir’s leadership, we won in Batley and Spen.

       “Keir will take us into the next election and I believe that result, in the early hours of Friday morning, is the start of more victories for Labour.”

       Labour’s candidate in Batley and Spen was Kim Leadbeater, sister of the seat’s former MP Joe Cox.

       Ms Cox was murdered by a far-right extremist in 2016, just days before the Brexit referendum.

       Her widower, Brendan Cox, told the BBC Ms Leadbeater had been “incredibly brave” to stand.

       He added: “It was a very bruising and pretty horrible campaign at times.”

       The Tories came second whilst George Galloway, representing the Workers Party of Britain, took third.

       There were ugly scenes during the campaign with some Labour canvassers being egged and physically assaulted.

       Mr Galloway, the former Respect Party MP, has voted to challenge the result in court.