Sadiq Khan makes a speech after he is re-elected for a record third time as Mayor of London, following the counting of votes, at City Hall in London, Saturday, May 4. AP-Yonhap

Sadiq Khan was re-elected as London's mayor, final results showed on Saturday, helping to cement the Labour Party's commanding lead over the governing Conservatives in local elections ahead of Britain's national vote later this year.

Khan's victory, his third in a row, was widely expected despite some public anger over knife crime and the Ultra Low Emission Zone (ULEZ), which charges drivers of older, more polluting vehicles a daily fee.

London is the latest of dozens of English councils and mayoralties that Labour has won in the local elections that took place on Thursday, inflicting heavy losses on Prime Minister Rishi Sunak's Conservatives.

"It's been a difficult few months, we faced a campaign of non-stop negativity," Khan said in a speech after the results showed he had won 43.8 percent of the vote against 33 percent for the Conservatives' candidate, Susan Hall.

"For the last eight years, London has been swimming against the tide of a Tory (Conservative) government and now with a Labour Party that's ready to govern again under Keir Starmer, it's time for Rishi Sunak to give the public a choice."

Opinion polls predict that Labour will win the next national election, propelling Starmer to power and ending 14 years of Conservative government in Britain.

Khan, 53, who became the first Muslim mayor of the British capital in 2016, has pledged to build more social housing and work with a future national Labour government to boost police capacity.

Hall had made scrapping ULEZ a centrepiece of her campaign but the 69-year-old Donald Trump fan made a series of gaffes and faced accusations of racism after being found to have engaged with far-right content online.

Campaigning against ULEZ had helped the Conservatives win a by-election to a parliamentary seat in London last year, while Sunak has also scaled back some of Britain's national climate goals, arguing that such targets shouldn't overburden voters.

Elsewhere in England, the result of the mayoral election in the West Midlands, which includes Birmingham, Britain's second largest city, was due later on Saturday.

The region's Conservative mayor Andy Street was expected to be re-elected but media reports said a recount of some votes was taking place, suggesting a close race.

Street ran a campaign which emphasised his personal record on investment while downplaying his Conservative Party affiliation. (Reuters)