Sir Keir Starmer has labelled Donald Trump’s warning about Sharia Law “ridiculous nonsense” as the Prime Minister defended London Mayor Sir Sadiq Khan from the US President’s United Nations swipe.

Sir Keir, who earlier this year looked to ease tensions between the White House and City Hall, also vowed to call out Mr Trump over his remarks when the pair next meet.

In a sit-down interview with ITV, the Prime Minister said: “There’s a few things we disagree about. This is one of them. The idea of the introduction of Sharia Law is nonsense.

“And Sadiq Khan is a very good man and actually driving down serious crime. So as I say, there’s a lot I agree with, with President Trump. We get along.

“We had a good state visit last week, but on this I disagree with him. The Sharia law comments were ridiculous.”

When pushed on whether he would call out Mr Trump, Sir Keir added: “Oh, of course, we have a frank conversation about many, many things.

“But I want to express my support for our mayor Sadiq Khan. We’re very proud to have a Muslim Mayor] in our diverse city.”

Sir Keir’s decision to condemn Mr Trump comes just two days after the US President’s rambling speech at the UN General Assembly in New York.

Mr Trump claimed that the UK “wants to go to Sharia Law” and described Sir Sadiq as a “terrible Mayor”.

Without pulling any punches, Sir Sadiq yesterday branded Mr Trump a racist, sexist and Islamophobe.

Sir Keir refused to repeat Sir Sadiq’s assessment of the US President.

“I’m absolutely clear, on the issues where I agree with the President, we have to work together,” the Prime Minister said.

“Of course, a very, very important relationship between our two countries.

“But equally, I’m very proud of our capital city and very proud of our Mayor here, who’s doing a very good job.”

Sir Keir has looked to avoid publicly criticising the US President since becoming Prime Minister.

Ahead of Mr Trump’s victory last November, Sir Keir and his then-Foreign Secretary David Lammy met with the property-tycoon-turned-politician in New York.

While Mr Lammy once labelled Mr Trump a “neo-Nazi sympathiser”, Sir Keir also condemned the US President during his time in opposition.

Speaking in January 2016, Sir Keir said: “What lies at the heart of his belief that Muslims should be banned is that he thinks they are all dangerous. That is not buffoonery. That is absolutely repugnant.”

Sir Sadiq’s spat with Mr Trump appears to have started at around the same time, with the London Mayor’s decision to allow protesters to fly a blimp of the US President sparking fury from the White House.

Despite Sir Keir’s concerns about Mr Trump’s previous comments, Reform UK leader Nigel Farage defended the US President over his recent outburst.

He said: “Is [Trump] right to say that Sharia is an issue in London? Yes. Is it an overwhelming issue at this stage? No.”

Sharia Law, which derives from the Koran, is the moral and legal framework that millions of Muslims follow.

It covers a broad range of topics that touch every aspect of a Muslim’s daily life, including religious practices, financial decisions and relationships.

Sharia law splits offences into two classes: “hadd” offences — serious crimes with penalties, and “tazir” crimes — for which the punishment is not fixed and up to the judge.

Hadd offences include theft and illicit sexual relations, which can be punishable by amputating the offender’s hand or foot under the sharia’s strictest interpretation.

Recent research has suggested that there are an estimated 85 Sharia courts operating in the UK.