Rebecca Long-Bailey will today vow to end the “gentlemen’s club of politics” and create a democratic revolution by devolving more power out of Westminster as she launches her bid to become the next Labour leader.

The remarks of the Shadow Business Secretary – one of four female candidates vying for the Labour crown – came as her main rival, Keir Starmer, insisted factionalism within the party had “got to go” and stressed Labour had to win back its heartlands in Scotland and Wales but also go further to win power.

Tomorrow, the contenders will engage each other in the first leadership hustings in Liverpool. This will take place as trade unions and local parties consider who to back; their decisions will prove crucial to which candidates’ names appear on the final ballot.

Ms Long-Bailey received a boost on Thursday when she won the endorsement of the radical Left Momentum group, which vowed to run "hundreds" of phone banks across the UK to secure her election.

Meanwhile, in the race for the deputy leadership, Ian Murray, Labour’s only Scottish MP following the SNP’s election landslide, launched his campaign at his old school in Wester Hailes, Edinburgh, urging the party to listen to the public or face becoming "a diminishing, perpetual Opposition".

He admitted to being “embarrassed” by Labour’s election campaign and performance, warning how "the architects of our past can't be the architects of our future".

The 43-year-old backbencher pledged to travel the length and breadth of the country to listen to voters as deputy leader, adding: "I will leave no stone unturned to produce a report that I will present to conference in September that says how we can win again and how we can win again together."

Ms Long-Bailey, who will launch her bid to succeed Jeremy Corbyn this evening in Manchester, will say: “The story of the last few years is that many people feel there is something wrong with their laws being drafted hundreds of miles away by a distant and largely unaccountable bureaucratic elite in Brussels. But I’ll be honest, Westminster didn’t feel much closer and it still doesn’t today.

“That’s why I want to shake up the way Government works and deliver a clear message to voters: we will put power where it belongs; in your hands.”

She will say the British state needs a “seismic shock,” to prise it open at all levels to the people, stressing: “We will end the gentlemen’s club of politics and we will be setting out plans to go further by devolving power out of Westminster to a regional and local level.”

The MP for Salford, 40, will add that she will fight for “modern, democratic public ownership” and for a Green New Deal to tackle the climate emergency.

Sir Keir, in an interview with the BBC, said Labour had spent too much time fighting itself rather than the Tories, declaring: “Factions have been there in the Labour Party; they've got to go.”

He insisted: "We need to unify the party and I think I can do that.”

The Shadow Brexit Secretary set out his mission to restore trust in the Labour Party as a “force for good and a force for change”.

Sir Keir said he was clear the Labour leader had to be able to speak for the whole of England, the whole of Scotland, the whole of Wales, and the whole of Northern Ireland.

“Because,” explained the 57-year-old London MP, “if all we do at the next election is win back our heartlands - and we need to, we need to address why we lost those heartlands - we will lose the next election.

“We need to win our heartlands back, we need to win in Scotland. We need to get back seats in Wales that we've lost. And we need to win in the south-east and the south-west. We need to win seats that we've lost to the Tories for many, many years.

“And so, we need someone who is able to, as it were, be capable of being respected and seen as someone who is trustable and trusted across the whole of the United Kingdom,” added the former Director of Public Prosecutions in England.