Sadiq Khan hails New York's first Muslim mayor as 'inspiring' after he is sworn in on Koran

Politicians from around the world were quick to praise Mr Mamdani, including the London Mayor, who congratulated the self-styled "democratic socialist" on his inauguration.

Sir Sadiq said: "In the face of hateful smears, anti-Muslim slurs and disinformation [Mr Mamdani] remained defiant and dignified. His response, meeting hate with hope and unity, inspired New Yorkers and many beyond. I wish him every success as he takes office."

In an interview with Politico, Sir Sadiq said he hoped to meet Mr Mamdani in the future, but the two had been communicating since his election.

He said: "We messaged and stuff, and he’s somebody who is clearly going to change discourse in not just America, but I think elsewhere...I think you’ll see the ripples of the Mamdani effect all across the globe."

However, he was blasted by the Your Party co-founder and former Labour MP Zarah Sultana, who made a jibe at Sir Sadiq and her former party.

She said: "Starmer’s Labour Party would’ve expelled Zohran Mamdani and you would’ve stayed silent about it."

In a speech following his public swearing-in, Mr Mamdani reiterated his campaign promises of universal childcare, affordable rents and free bus service.

He told the crowd: "We will answer to all New Yorkers, not to any billionaire or oligarch who thinks they can buy our democracy. I was elected as a democratic socialist and I will govern as a democratic socialist."

Mr Mamdani's inauguration included remarks by veteran socialist US Senator for Vermont Bernie Sanders and New York Representative Alexandria Ocasio-Cortez.

Mr Sanders said: "Making sure that people can live in affordable housing is not radical...It is the right and decent thing to do."

Republicans were quick to attack Mr Mamdani, describing the 34-year-old as a "radical socialist".

A spokesman from lead group tasked with electing GOP politicians to the US House of Representatives said: "Every time Mamdani opens his mouth or swipes his pen, he tattoos the Democrat Party’s failures onto every House Democrat facing voters in 2026."

Uganda-born Mr Mamdani has been a harsh critic of President Donald Trump on issues such as immigration, adding his differences with Republican were numerous, despite a warm meeting between the two in November.

Mr Mamdani inspired a record-breaking turnout of more than two million voters and took 50 per cent of the vote in November, nearly 10 points ahead of Mr Cuomo running as an independent and well ahead of Republican Mr Sliwa.

In his address, Mr Mamdani pledged to transform the New York Government on behalf of the city's struggling working class.

He told cheering crowds: "Beginning today, we will govern expansively and audaciously. We may not always succeed, but never will we be accused of lacking the courage to try.

"To those who insist that the era of big government is over, hear me when I say this: No longer will City Hall hesitate to use its power to improve New Yorkers' lives.

"I will not abandon my principles for fear of being deemed 'radical.'"

Sir Sadiq Khan wasn't the only British politician to heap praise on Mr Mamdani.

Green Party Leader Zack Polanski called it a "delightful moment where hope has triumphed", while a joint statement between Your Party co-founders Jeremy Corbyn and Ms Sultana said his victory showed: "The old politics of the centre is bankrupt and a new socialist politics can take its place."

Others within Labour were more sceptical.

One influential party figure told the BBC: "I'll tell you what, I cannot be doing with all the takes we'll get on this New York mayor and what it means for the Labour Party."

Our Standards: The GB News Editorial Charter