Sadiq Khan’s election victory as London mayor has “bucked the trend” of Muslim voters turning away from Labour over the party’s stance on the war in Gaza, party figures said.

The 53-year-old won a third term as the capital’s mayor on Saturday, without seeming to have lost the support of large numbers of Muslim voters – unlike Labour candidates elsewhere in England last week.

But Labour candidates elsewhere in England last week saw a significant loss of Muslim voters. Richard Parker became West Midlands mayor after a knife-edge contest with Andy Street, but it would have been much easier for the Labour man had substantial numbers of voters not backed an independent candidate whose campaign focused on Gaza.

Akhmed Yakoob, a criminal defence lawyer, came third with 42,923 votes in Birmingham alone, where Parker saw a major decline on Labour’s 2021 vote.

In contrast, Khan defeated his Conservative rival Susan Hall by 275,828 votes, a comfortable 11% margin.

“We faced a campaign of nonstop negativity, but I couldn’t be more proud that we answered fear-mongering with facts, hate with hope and attempts to divide with efforts to unite,” Khan said in his victory speech.

He also thanked his family and told them: “Some of the stuff on social media, the protests at my home, the threats – it’s upsetting, it’s frightening and it’s wrong. I’m truly sorry for putting you through this.”

Labour supporters had been concerned that the mayor might suffer a Gaza backlash, opposition in outer London to the ultra-low emission zone (Ulez), and a switch from a supplementary vote system to first-past-the-post, even though a YouGov poll last week put Khan on 47%, well ahead of Susan Hall, on 25%.

After the votes were counted, Ulez appeared to have had little effect, but the mayor did well in the two constituencies with higher numbers of Muslim voters.

In North East, which includes Waltham Forest, Khan got 127,455 votes compared with 111,359 first preferences in 2021, while in City and East, which includes Newham and Tower Hamlets, the turnout fell by 30,000, but Khan had nearly 10,000 more votes than first preferences in 2021.

The emphatic win ran counter to reporting by the BBC and other media outlets, who had claimed the race was close. Torsten Bell, chief executive of the Resolution Foundation thinktank, wrote on X on Saturday: “1pm BBC news still reporting ‘evidence that London closer than expected’ despite literally zero evidence – now or at any point over the last 24hrs.” “Should have been a VERY high evidence bar for thinking this was close,” he added.

Khan was among the earliest Labour figures to call for a ceasefire in Gaza, in contrast to the Labour leader, who was hit by several defections and resignations after he said last October that Israel had “the right” to withhold power and water from Gaza.

There was a furious reaction from those on the left, which has continued to simmer. At the most recent Palestine Solidarity Campaign march in London last month, the most obvious political placards were demonic cut-outs of Starmer and deputy leader Angela Rayner, dubbed Starmer for Genocide and Angela of Death.

Ali Milani, the national chair of the Labour Muslim Network and a former Labour councillor who stood against Boris Johnson in Uxbridge in 2021, said that many Muslim voters had felt betrayed by Labour’s stance on Gaza.

“This is something I’ve been warning about for months and it’s no longer polls and speculation – it’s real-life votes,” he said. “Whether it’s Oldham or Bolton, Birmingham or Elswick in Newcastle, there’s no question now there’s a serious problem.

“Sadiq is bucking the trend and there’s a reason for that. He was very early in calling for a ceasefire. He is now supporting a suspension of arms sales, as long as it’s clear that international law has been breached. So he did what we should have done and reaped the electoral rewards for that.

“Unfortunately, and it pains me to say it, Muslims don’t think that the Labour party broadly values Palestinian and Muslim lives as equal to others. And nothing encapsulates that better than the message we’ve been sent around the country in other seats and constituencies and mayoralties.”

At last week’s polls, this translated into a 17.9% drop in the Labour vote in areas where more than a fifth of people identified as Muslim, according to Professor Will Jennings of Southampton University.

Although Labour gained control of eight councils, it lost seats and lost control of Oldham council in Greater Manchester. It failed to regain Oxford, lost ground in Blackburn with Darwen and Bradford, while the Workers Party of Britain, founded by George Galloway, unseated Manchester council’s deputy leader Luthfur Rahman.

A Momentum spokesperson said the defeats should be “a wake-up call for the Labour leadership” and said Starmer should call for a suspension of arms sales to Israel. It said: “Any party which takes its core vote for granted risks disaster sooner or later. When the going gets tough, Labour will need to rally its base – but from climate to Gaza, Keir Starmer couldn’t seem less interested.”

Sunder Katwala, director of British Future, said there had been a bigger impact on Labour’s vote during the local elections than had been showing up in national polling, but there might not be much effect on its chances in a general election.

“Labour’s general election plan is going very well, according to these local election results, because it’s advancing in lots of places where Labour isn’t strong,” he said.

However, since council wards were a fraction of the size of constituencies, they could be more easily dominated by particular groups than parliamentary constituencies. “There are a few hundred council seats where the Muslim voter group is the majority of a council ward. But that’s true of only three Westminster constituencies,” he said.

Katwala added that Palestine was unusually prominent compared with other foreign policy issues among voters’ concerns, but that there was no single bloc of Muslim voters. “People exaggerate the number of Muslim voters and the way they vote in a bloc,” he said. “These results look quite like the post-Iraq impact of 2005. It was not that Muslims were voting as a bloc, but that Muslim votes were breaking up much more than ever before.”

• This article was amended on 5 May 2024. An earlier version said that the London mayoral electoral system had changed to first-past-the post for this election from “proportional representation” when in fact previously it had been a supplementary vote system.