Sadiq Khan has been elected mayor of London, winning a historic third term after a dramatic contest.

Khan was declared the winner over the Conservative candidate, Susan Hall, on Saturday afternoon, with 43.8% of the vote.

The London mayor was booed as he began his victory speech. “Thank you from the bottom of my heart, thank you, London,” he told an audience at City Hall before a heckler walked across the stage shouting, “Khan killed London.”

He pressed on, noting: “It’s been a difficult few months. We faced a campaign of non-stop negativity,” but went on to praise his team for leading a campaign that responded to “fearmongering with facts, hate with hope, and attempts to divide with unity”.

Hall, his rival, appeared stony-faced as Khan made his speech, and slightly shook her head in disapproval as Khan told the crowd he would be a mayor for all Londoners, including those who did not vote for him.

Khan had described the battle as a “close two-horse race” when polls predicted he had a 25-point lead over his Tory rival, in what appeared to be an effort to encourage Labour loyalists and more apathetic Londoners to vote.

According to London Elects, which manages the mayoral and London assembly elections, voter turnout was only 1.5% down on 2021, at 40.5%. Bexley and Bromley, led by the Conservatives, had the highest constituency turnout with 48%.

Khan’s team became confident of winning the race after Labour took the North East and West Central constituencies from the Conservatives.

On Saturday morning, the Labour leader, Keir Starmer, had said he was confident of Khan’s victory and described the mayoral race as “effectively the last stop on the journey to the general election”.

Speaking in Mansfield, in the East Midlands region that has selected the Labour candidate as its first mayor, Starmer said: “He [Khan] has got two terms of delivery behind him and I am confident that he has got another term of delivery in front of him.

“But look, if you look across the country, I am standing here in Mansfield in the East Midlands, where we have won a significant victory in the mayoralty here, but that is the pattern across the country.”

The victory in London followed a tense Friday night, described by Labour sources as a “24-hour vacuum” because a pause on London mayoral counts had enabled “excited” Tory activists to fill social media with rumours of polling predictions being “completely wrong” and Hall posing a much greater threat. It led some Labour insiders to believe the possibility that the candidates could be a few points apart.

This mayoral election was the first held after changes to the voting system that were introduced by the Conservatives. It had been made into a first-past-the-post contest with photo ID required at polling stations, measures that had been expected to harm Labour’s vote.