Donald Trump has arrived in the UK for a delayed state visit and set a combative tone by criticising the London mayor as his plane landed.

After Air Force One touched down at Stansted, the US president and his wife, Melania, were greeted by the foreign secretary, Jeremy Hunt, one of the contenders in the Conservative leadership race.

Trump was seen chatting with Hunt for a minute and occasionally patting him on the back.

Before landing, Trump described Sadiq Khan as “a stone cold loser” after the London mayor compared him to a 20th-century fascist.

Donald J. Trump (@realDonaldTrump) .@SadiqKhan, who by all accounts has done a terrible job as Mayor of London, has been foolishly “nasty” to the visiting President of the United States, by far the most important ally of the United Kingdom. He is a stone cold loser who should focus on crime in London, not me......

Donald J. Trump (@realDonaldTrump) ....Kahn reminds me very much of our very dumb and incompetent Mayor of NYC, de Blasio, who has also done a terrible job - only half his height. In any event, I look forward to being a great friend to the United Kingdom, and am looking very much forward to my visit. Landing now!

Trump repeated his criticism about Khan to Hunt as they spoke on the tarmac, said the foreign secretary, who told BBC News: “I said to him that we were going to put on a great show for him, because America is our closest ally.

“And he mentioned to me some of his very strong views about the mayor of London. What he said to me was consistent with what was in his tweet.”

Hunt added: “I agree with him that it is totally inappropriate for the Labour party to be boycotting this incredibly important visit. This is the president of the United States.”

Khan’s spokesman said “childish insults” should be “beneath the president of the United States”.

Tens of thousands of protesters are expected to take to the streets to demonstrate against the visit. As he waited to greet Trump, Hunt was distinctly muted in his welcome, declining twice to disagree with a description of the US president’s policies as “toxic and dangerous”.

Asked about the remarks by the bishop of Liverpool, Paul Bayes, Hunt told BBC Radio 4’s Today programme: “People will have their own views about President Trump’s politics. He’s very controversial.”

Asked again whether he disputed Bayes’ description, Hunt said: “I don’t pretend that I personally agree with Donald Trump on everything. But he’s also president of our most important ally. He’s coming here to celebrate what is the most important alliance in history.”

The foreign secretary indicated Trump and Theresa May might not have a one-to-one discussion during meetings on Tuesday, seen as an indication of the imminently departing prime minister’s status.

Q&A Itinerary: What will Trump be doing during his UK state visit? Show Hide After arriving in the UK on Air Force One on Monday 3 June, US president Donald Trump will be formally welcomed in a ceremony in the gardens of Buckingham Palace. It will be attended by the Queen and Prince Charles. The president will then attend a private lunch at the palace, which is expected to be attended by Prince Harry, but not his wife, who Trump recently described as 'nasty'. Following a wreath-laying ceremony in Westminster Abbey, Donald Trump will join Prince Charles for an afternoon tea at Clarence House. The Queen, Prince Charles and Prince Harry will then host a state banquet in the evening, which will be attended by prominent US citizens who live in the UK, as well as political and civic leaders. On Tuesday 4 June the visit includes a breakfast meeting with Prince Andrew, and then talks and a press conference with prime minister Theresa May at Downing Street. On the Tuesday evening Trump hosts a dinner at the residence of the US ambassador. On Wednesday 5 June Trump will take part in commemoration services in Portsmouth to mark the 75th anniversary of the D-Day landings. The day ends with the Queen formally bidding farewell to the US president. Trump’s entourage will also include two identical seven-seat black armoured limousines nicknamed ‘The Beast’, and a number of presidential helicopters. The president has at his side at all times one of five rotating military aides who carry the nuclear ‘football’ which can trigger a missile strike - equipped with communication tools and a book with prepared war plans. Photograph: Jonathan Ernst/X90178

“He’s going to sit down with Theresa May in a meeting which I will be at, and he may well sit down with her one to one, as often happens, before or after those meetings,” Hunt said.

Before his flight to the UK, Trump praised Hunt’s main rival, Boris Johnson, and the Brexit party leader, Nigel Farage, and denied making “bad” comments about the Duchess of Sussex.

The US president said he expected his three-day visit to be “very important” and “very interesting”.

Play Video 0:49 Trump praises Boris Johnson and Nigel Farage ahead of UK visit – video

Speaking to reporters on Sunday before boarding the Marine One helicopter, Trump was asked if he planned to meet Johnson during the trip.

“Well, I think I may meet with him. He’s been a friend of mine. He’s been very nice. I have a very good relationship with him,” he said of the Tory leadership hopeful.

“I have a very good relationship with Nigel Farage, with many people over there [in the UK], and we’ll see what happens. I may meet with him. They want to meet. We’ll see what happens.”

Before his arrival, the US president had already caused considerable political turbulence with comments on the Conservative leadership race, Brexit and Meghan, Duchess of Sussex.

Facebook Twitter Pinterest Jeremy Hunt points as he waits for Donald Trump’s plane to land at Stansted. Photograph: Hannah McKay/Reuters

Trump said he did not call Meghan nasty, despite audio recordings in which he said “I didn’t know she was nasty” when he was told she had said she would leave the US if he won the 2016 election.

Asked at the White House on Sunday evening if he was willing to apologise to the royal family, or clarify his comments, Trump replied: “No, I made no bad comment. Thank you.”

He had called on Britain to leave the EU without a deal if Brussels refused to meet its demands, and urged the government to send Farage into the negotiations.

The controversy was further exacerbated on Sunday when the US ambassador to the UK, Woody Johnson, suggested the NHS would be on the table in post-Brexit trade talks with Washington.

Facebook Twitter Pinterest Woody Johnson speaks on The Andrew Marr Show on Sunday. Photograph: Jeff Overs/BBC/Getty Images

Addressing the prospect of a transatlantic trade deal, Trump said: “[We’re] going to the UK. I think it’ll be very important. It certainly will be very interesting. There’s a lot going on in the UK. And I’m sure it’s going to work out very well for them.

“As you know, they want to do trade with the United States, and I think there’s an opportunity for a very big trade deal at some point in the near future. And we’ll see how that works out.”

The president departed from Joint Base Andrews near Washington DC onboard Air Force One at about 8.45pm local time (1.45am BST).

The Trumps are due to head to Buckingham Palace for a reception with the Queen, the Prince of Wales and the Duchess of Cornwall.

Facebook Twitter Pinterest The ‘Trump baby’ blimp at a protest during his visit last year. Photograph: Peter Nicholls/Reuters

Prince Harry will also attend a private lunch at the palace, although his wife, Meghan, who is on maternity leave, will be at home with their four-week-old son, Archie.

Trump’s arrival in the capital is due to be followed by a protest through central London on Tuesday, with the “Trump baby” blimp made for his visit last year due to put in an appearance.

On Sunday, Khan described the US president as “just one of the most egregious examples of a growing global threat” and compared the language he has used to that of the “fascists of the 20th century”.

Asked if he would be willing to meet the London mayor, Trump replied: “No, I don’t think much of him. I think that he’s the twin of [the New York City mayor Bill] de Blasio, except shorter.”

Play Video 1:50 Sadiq Khan to Trump: you stand for the opposite of London's values – video

With the Press Association