Votes are being counted in the Batley and Spen by-election with Labour braced for defeat and Sir Keir Starmer’s leadership of the party certain to come under intense pressure.

The party is defending a majority of more than 3,000 in the seat but the bookies have the Conservatives as odds-on favourites to follow up their victory in Hartlepool in May.

A result is expected early on Friday morning and one Labour source predicted a “long night” for the party, while another said the campaign had been a shambles.

Meanwhile, deputy leader Angela Rayner denied she was part of a possible bid to challenge Sir Keir if the party loses the West Yorkshire seat.

Sir Keir’s spokesman has insisted he will not resign if Labour loses but new polling this week suggested as many as four in 10 party members would want him to quit in the wake of a loss.

The by-election was seen as a straight fight between Labour’s Kim Leadbeater and the Tories’ Ryan Stephenson, but the arrival of veteran campaigner George Galloway in the constituency provided an extra headache for Labour’s campaign managers.

Mr Galloway said he was targeting Labour voters in an explicit attempt to topple Sir Keir during a campaign which became increasingly bitter.

A Labour source said: “Galloway’s nasty campaign has hit our vote while the Tories are picking up 2019 independent votes, and places that were starting to look more positive for us seem to have swung back.

“It’s going to be a long night.”

One Labour frontbench MP predicted a 6,000-vote majority for the Tories and described the campaign as an “utter shambles” with “loads of switchers” to Boris Johnson’s party.

Ms Leadbeater referred to the occasionally ugly nature of the contest in a message on Twitter.

“There have been many highs of this election campaign but sadly there have also been some unacceptable lows,” she said.

“The acts of intimidation and violence by some who have come here with the sole aim of sowing division has been deeply upsetting to witness.

“Whatever the result tonight, the first priorities of the new MP must be to bring our community together and start working for local people in every part of the constituency I am proud to call my home.”

Tory insiders played down expectations as polls closed, insisting it was “too close to call”.

A Conservative source said it was “always was going to be tough – we didn’t win in 2019 and we lost by over 100,000 votes in the West Yorkshire mayoral race”.

“On top of that, governing parties don’t normally win by-elections,” the source added – although Hartlepool showed Mr Johnson’s party was capable of making further cracks in Labour’s northern Red Wall.

Mr Stephenson said: “Whatever the result, you proved that more and more local people are ready for change.”

Mr Galloway said: “One thing is certain: it’s curtains for Keir.”

Turnout in the by-election was 46.7%, Kirklees Council said.

The Batley and Spen contest saw clashes between Mr Galloway’s Workers Party and Labour supporters.

The most controversial arguments centred on the parties’ stance on international issues, including Kashmir and Palestine, as they battled to secure votes in the area’s Asian communities.

The nature of the campaign was particularly sensitive as Ms Leadbeater is the sister of former Batley and Spen MP Jo Cox, who was murdered in the constituency in 2016.

Labour activists said they were pelted with eggs and kicked in the head on the campaign trail at the weekend and West Yorkshire Police said an 18-year-old man from Batley was arrested on suspicion of assault in connection with an attack on canvassers.

A defeat for Labour would lead to further questions about Sir Keir’s position, although it is unclear if any challenger would be able to secure the support of the 40 MPs needed to trigger a leadership contest.

The Times reported an individual described as a “close ally” of Ms Rayner as saying: “There’s definitely been people sounding out the possibility — it’s clear she’d easily reach 40 nominations — and urging her to run if the worst happens in Batley.”

Ms Rayner described the suggestion as “news to me”, while her spokesman said anyone gauging support is “not doing it under instructions from Angela or with Angela’s backing” and she is “focused entirely on her jobs”.

One senior Labour MP suggested Sir Keir would be given until the Labour conference in September to turn the situation around if there was a defeat in Batley and Spen.

The West Yorkshire constituency has voted Labour since 1997, but a Survation poll published last week put the Tories on 47%, up 11% from the 2019 general election, while Labour was on 43%.

The by-election was triggered after Tracy Brabin, who won the seat for Labour in 2019 with a 3,525 majority over the Conservatives, was elected as the mayor of West Yorkshire in May.