The mayor of London, Sadiq Khan, who is frequently the target of Donald Trump’s most vituperative tweets, has hit back at the US President when appearing at the Edinburgh Fringe on Friday.

Sadiq was quizzed about Trump during an interview with broadcaster Iain Dale at the cultural festival. “I have no idea what Donald Trump has against the Muslim mayor of London,” quipped Sadiq.

Among other insults, the President has called Sadiq a “stone cold loser who should focus on crime in London” and “a national disgrace who is destroying the city of London!”

Now it was Sadiq’s turn to describe the President as “the poster boy for the far-Right, racist movement around the world”. He said: “We’ve all got to be vigilant to the fact that you’ve got the President of the USA who has views that are paraded by terrorists in Christchurch, by terrorists in El Paso, by terrorists in this country and by terrorists all over the world. That should worry us.

“I challenge you to find any tweet that I’ve done proactively saying anything about Trump. In fact, the man’s obsessed with me — I’m seriously worried.

“I’m the mayor of London, I’m quite busy and haven’t got the time to check my Twitter, let alone take the time to respond.

“This guy is President of the USA and if you get the chance, count how many times he’s tweeted about me.”

Jokes aside, Trump could damage Sadiq’s re-election prospects during the mayoral elections next summer, not least because London has witnessed a surge in knife crime, with 132 people — many of them young black men — stabbed to death last year and the 100 figure crossed as early as May this year.

Boris Johnson has promised to recruit an additional 20,000 police officers but the fall in their numbers, Sadiq argued, has been brought about by Tory budget cuts.

Sadiq branded the new Prime Minister a “liar” who has filled his cabinet with ministers who have “seriously obnoxious views”.

“I’m 48 years old and I can’t remember a more Right-wing government in my lifetime. There are people in his cabinet that have got seriously obnoxious views about a whole host of issues.

“The problem with all of us who are critical of Boris Johnson is that we get bought in by the buffoon trick and the problem is the consequences are going to be catastrophic if we leave the EU without any deal.”

Sadiq’s comments about Boris come against the background of increasing speculation that the Prime Minister will call an early general election — but that he will take Britain out of the EU by October 31 even after losing a no confidence motion in the Commons.

There is also a growing worry that in such circumstances, the Queen will be pressed by Labour and other Opposition MPs to dismiss Boris if he refuses to resign.

Saturday’s Daily Telegraph reported that cabinet secretary Sir Mark Sedwill has discussed how the Queen can be kept out of a possible constitutional crisis with her private secretary, Edward Young.

Incidentally, Boris, whose Telegraph column in the past has caused offence by describing Muslim women in burqas as resembling “letter boxes” and “bank robbers”, issued a placatory message on the occasion of Id ul-Zoha.

He said: “Whether you’re one of Britain’s 3.3 million Muslims, or one of more than a billion people worldwide celebrating Id ul-Zoha this week, I want to take this opportunity to say Id Mubarak to you all.

“In business, in our public services, in culture and the media, at the highest levels of government and of course in England’s World Cup-winning cricket team, British Muslims are helping to make this country the success it is today.”