Sir Keir Starmer has declared “Labour is back” as he told his party the Batley and Spen by-election win shows what can be achieved when it “pulls together”.

The Labour leader joined the UK’s newest MP, Kim Leadbeater, in the West Yorkshire constituency on Friday following her victory by 323 votes over the Conservatives.

The result eases the pressure on Sir Keir, who could have been left facing further questions over his leadership of Labour – and even a possible leadership challenge – had the party not held the seat.

And, asked what his post-victory message was to his party, Sir Keir said: “My message is, when the Labour Party sticks to its core values, is rooted in its communities and pulls together, we can win just as we’ve won here.

“This is the start, Labour is back.”

Adapting the refrain of England football supporters during Euro 2020, Sir Keir also told supporters in the constituency: “This is just the start. I want many more days like this. Labour is coming home.”

The Labour leader has faced a bruising few months, following a disappointing set of local election results, defeat in the Hartlepool by-election and a poor showing in last month’s Chesham and Amersham contest.

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It had led to suggestions that critics of Sir Keir on Labour’s left were plotting a leadership challenge should the party have lost in Batley and Spen.

But, when it was suggested that Ms Leadbeater had “saved his skin”, Sir Keir said the by-election win was “a victory for the whole Labour movement”.

“Of course it’s a special victory for Kim – she’s a fantastic candidate and what she offers is incredible and I pay absolute tribute to her,” he said of Labour’s winning candidate, who is the sister of murdered MP Jo Cox.

“But this is a victory for the Labour movement and it has filled everybody’s hearts with hope that those values, those core Labour values can win out and they will win out.”

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Sir Keir also appeared to agree with the admission by Conservative co-chair Amanda Milling that the scandal over ex-health secretary Matt Hancock’s affair had harmed the Tory campaign.

“I think people are getting fed up with the politics of misinformation, half-truths, untruths and division,” he said.

“And what they want is what Kim can give them, which is positivity, which is bringing communities together.

“She’s of her community, she’s for her community. It’s about decency and integrity versus misinformation, manipulation, lies and half-truths.”

The Batley and Spen by-election was one of the fiercest to be fought in recent years, with the contest marked by allegations of violence and dirty tricks.

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Former MP George Galloway and his Workers Party of Britain – who had fought against Labour in Batley and Spen with the aim of toppling Sir Keir – came third with 8,264 votes.

He has since vowed to legally challenge the result.

“Let’s not beat about the bush – the divisive politics took probably 8,000 votes from Labour,” said Sir Keir when he was challenged about the narrow margin with which Ms Leadbeater won.

“So there was an attempt to divide the Labour vote and yet Kim won.”

He added: “One thing of real significance here is that Kim has won this because Tories in Batley and Spen, former Tory voters, voted for her.

“The left vote, if you like, the Labour vote was split but we won. The Tories had a clean hit, nobody was going against them, and they didn’t win.

“They expected to win this, make no mistake about that.”

Earlier, Ms Milling had acknowledged that Mr Hancock’s breaching of coronavirus restrictions – he was captured on video kissing an aide in his office – had prompted concern from voters in West Yorkshire.

“It was something that came up on the doorstep, I have to be honest about that,” she told Sky News, although she added there were “a whole host of different issues that came up”.