Who said this, exactly a year ago? “I recognise that at the last mayoral election and at the general election, there were many Jews who felt they simply couldn’t vote Labour. Being a Jewish Londoner in 2015 is a challenge. I didn’t fully understand the scale of anti-Semitism”.

Well done and a packet of (kosher) crisps to anyone who recognised the words of the man who is now London’s mayor, the former MP for Tooting, Sadiq Khan.

From a Jewish standpoint Khan came trailing some dubious baggage. He had been the UK lawyer for the notorious Nation of Islam leader Louis Farrakhan, who had made many anti-Semitic comments, including a suggestion that Jews were responsible for 9/11.

And, much more to the point, Khan was one of the MPs who nominated Jeremy Corbyn to be leader of the Labour Party, ensuring his name was on the ballot paper “in the interests of diversity and a wider debate”.

A year on and Sadiq, like all of us, has had some hard lessons to learn about Labour politics, and, in particular, the coterie surrounding the inner leadership of Her Majesty’s Opposition. Intelligently, the mayor, true to his pre-election pledges, has been keeping his head down and not engaging in the rough-and-tumble of Labour’s drawn-out public suicide. Tempting though it must have been, Mayor Khan said nothing when his Labour predecessor, Ken Livingstone, became embroiled in an utterly unnecessary row about Hitler; and he said nothing about the farrago involving a peerage for his fellow lawyer, Shami Chakrabarti, in a suggested quid pro quo for giving Labour a relatively clean slate over anti-Semitism.

This, the mayor evidently decided, was not mayor of London business, and in that regard Londoners have cause to be grateful, since what Londoners quite clearly want is a mayor who pays attention to London’s needs and not someone giving a running commentary on the political lunacies of the day.

Mr Khan must also, privately, have had cause to thank his lucky stars that Jeremy Corbyn was not his ultimate boss, for although Sadiq Khan won the election on a Labour ticket, there is no doubt in my mind that he won an enormous number of personal votes from people who, because of Jeremy Corbyn, could barely bring themselves to vote for Labour. So here we sit, a storm-tossed year later, on the eve of yet another race for the Labour leadership, and the mayor’s patience has finally snapped.

Over the weekend, Sadiq Khan outlined why – even though he apparently continues to believe in Corbyn’s standing as a pillar of the Labour Party ­­– he cannot support him to remain in post. Explaining his decision to support Owen Smith as leader, he wrote: “Jeremy has proved that he is unable to organise an effective team, and has failed to win the trust and respect of the British people.”

And if you’re wondering what this has to do with the Jewish community, I am sorry to have to direct your attention to a poisonous debate playing itself out on social media.

Over a picture of Sadiq Khan wearing a kippah and holding a piece of matzah –presumably at some interfaith seder –some keyboard charmer has asked: “Who owns you, Sadiq Khan?” In other words, support for Owen Smith, instead of Corbyn, is tantamount to throwing your lot in with the Jews.

I’d like to think that the mayor’s intervention will have some resonance outside City Hall and that his plainly heartfelt distress about what Corbyn is doing to the Labour Party will be echoed elsewhere.

But you know what? Even if Khan is wrong, and Corbyn does get re-elected, a gauntlet has now been thrown down by the mayor. No more Mr Nice Guy when it comes to dealing with Corbyn’s Labour, which, horrifyingly, looks as though it might be on the verge of letting both Livingstone and Galloway back into the party. And throwing your lot in with the Jews is not so bad, really. We don’t own the mayor, but luckily, nor does Jeremy Corbyn.