It was not even particularly close. In the final round of voting, Sadiq Khan beat Tessa Jowell by 59% to 41%.
It is a surprise because Jowell, the former culture secretary who oversaw London’s successful 2012 Olympics, and who is widely liked in the party, was the favourite throughout the campaign, according to polls showing the views of Labour supporters in London.
But the Jowell camp started to worry in the early summer when it became clear that enthusiasm for Jeremy Corbyn was leading to a surge in people signing up to take part, either as new members or registered supporters.
Khan is no Corbynite leftwinger, but he was one of the MPs who nominated Corbyn to help get him on the ballot paper and his soft left, Ed Miliband-ite politics are more palatable to the Labour newcomers than Jowell’s.
For some, Tony Blair and the Iraq war will have been a factor too. Khan did not vote for the war, because he was not elected until 2005, and he has been critical of the war, while Jowell famously once said she would throw herself under a bus for the former prime minister.
Friday’s result will reinforce the impression that Labour’s new selectorate is about to deliver a resounding victory for Corbyn on Saturday.
But the read across is not exact, as some London Labourites were voting Jowell and Corbyn. In 2010, London Labour voted for David Miliband as leader but for Ken Livingstone as mayoral candidate.
And it would be a mistake to assume that leftishness was the only, or even the main, factor behind Khan’s success. With support from the unions, Khan ran a formidably well organised campaign.
Perhaps just as importantly, with the Tory candidate almost certain to be the millionaire old Etonian Zac Goldsmith, many Labour members will have felt that a Muslim bus driver’s son, bought up on a council estate, would have made a better contrast than a white former cabinet minister married to a wealthy lawyer.
This article was written by Andrew Sparrow, for theguardian.com on Friday 11th September 2015 13.32 Europe/Londonguardian.co.uk © Guardian News and Media Limited 2010