Labour has won the Batley and Spen by-election, a victory that will come as a huge relief to Keir Starmer amid rumours a loss could have triggered a leadership challenge.

Kim Leadbeater won the West Yorkshire seat with a majority of just 323 – down from the 3,525 vote cushion the party had in 2019 – but the result was a surprise after opinion polls put the Tories in the lead and Labour insiders had feared the worst.

The victory will ease the pressure on Starmer, who had faced questions about his leadership after the loss of Hartlepool in a by-election in May, and will boost morale within Labour.

Leadbeater secured the seat with 13,296 votes, with Tory Ryan Stephenson on 12,973 and George Galloway – who had targeted Labour voters and campaigned to topple Starmer – in third with 8.264.

The result means Leadbeater now represents the seat previously held by her sister Jo Cox, who was murdered in the constituency in 2016.

Starmer hailed the “fantastic result” for the “brilliant and brave” Leadbeater after a contest marred by allegations of dirty tricks and violence.

Leadbeater said she was “absolutely delighted that the people of Batley and Spen have rejected division and they voted for hope”.

Leadbeater thanked the police “who, sadly, I have needed more than ever over the last few weeks” and her family, saying that “without them, I could not have got through the last five years, never mind the last five weeks”.

“I want to give a special shout out to my niece and nephew who I cannot wait to hug as soon as I see them,” she said, in an apparent reference to Cox’s two children.

Cox’s widower Brendan tweeted: “We are all incredibly proud of @kimleadbeater today and Jo would have been too”.

“The people of Batley & Spen have voted for decency and positivity once again,” he 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.

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.

The result will offer some breathing space to Starmer amid speculation about a possible leadership challenge in Westminster.

Ahead of the contest his allies said he would not quit if Labour had lost, but reports had suggested supporters of deputy leader Angela Rayner were plotting a move against him.

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”.

Following the result, Rayner offered her congratulations to Leadbeater “and the whole Labour team”.