From left, first lady Melania Trump, President Donald Trump, British Prime Minister Theresa May and her husband Philip May watch the arrival ceremony at Blenheim Palace, Oxfordshire, Thursday, July 12, 2018. (AP Photo/Pablo Martinez Monsivais)

LONDON | The British pound fell and U.K. politicians reeled Friday from the tornado-blast of U.S. President Donald Trump, who humiliated Prime Minister Theresa May, dashed hopes of a quick U.S.-U.K. trade deal and praised May’s opponents in the high-stakes battle over Brexit.

All in just 24 hours in Britain.

In an interview with The Sun newspaper, Trump slammed May’s plans for Britain’s departure from the European Union and praised her political rival Boris Johnson, who quit May’s Cabinet this week over Brexit differences. He also criticized immigration in Europe and declared that London Mayor Sadiq Khan, a Muslim, had failed to stop terrorism.

The pound fell 0.6 percent to $1.31 after Trump’s comments, and May’s government struggled to put a brave face on a presidential visit that has veered wildly off course.

“Trump claimed that Theresa May’s current Brexit plan ‘will probably kill’ any potential U.S. trade deal, a comment that not only undermines the prime minister at the end of an already challenging week, but one that understandably sent sterling sharply lower,” said Connor Campbell, an analyst at SpreadEx.

In Britain, where vicious differences are often masked by formal politeness, many politicians expressed shock that the U.S. president could be so downright rude.

In one of the milder responses, Universities Minister Sam Gyimah tweeted: “Where are your manners, Mr. President?”

Labour Party foreign affairs spokeswoman Emily Thornberry said “Donald Trump ought to have listened to his mother.”

“I am assuming that his mum told him that when you go to someone’s house you do not insult the host,” Thornberry said.

Trump’s Brexit broadside came as May was trying to shift stalled divorce negotiations with the EU into higher gear. Britain will leave the bloc in March, but the two sides have not yet agreed on what sort of relationship they will have after that.

On Thursday, as Trump flew into Britain, May’s government published a plan that includes free trade in goods and a common trade rule book with the EU.

Trump said such a deal “will probably kill” any prospect of a U.S.-U.K. free-trade agreement. Boosting trans-Atlantic trade ties was one of Britain’s main goals for Trump’s first official visit to the U.K. as president.

May was hosting Trump for talks Friday at her country residence, Chequers, over a lunch of Dover sole, Chiltern lamb and lemon meringue pie.

Trump and his wife Melania will also have tea with Queen Elizabeth II at Windsor Castle later Friday.

With considerable optimism, Treasury chief Philip Hammond said May was looking forward to her talks with the president.

“I’m sure there will be a very positive discussion,” he said.

But the truth is that Trump’s attack could weaken May’s already fragile hold on power. Her Conservative government is deeply split between supporters of a clean break with the EU and those who want to keep close ties with the bloc, Britain’s biggest trading partner.

Brexit Secretary David Davis and Johnson, the former foreign secretary, both quit this week to protest May’s trade plan. Johnson, who helped lead the campaign to take Britain out of the EU, accused May of killing “the Brexit dream.”

In his interview, Trump praised Johnson — another unpredictable, talkative populist with a distinctive mop of hair.

“I think he would be a great prime minister. I think he’s got what it takes,” Trump said.

Trump also renewed his attack on Khan, London’s mayor. The two politicians have clashed on Twitter over Trump’s ban on immigrants from several mostly Muslim countries and on the president’s views on crime and terrorism in Britain.

Trump claimed that London’s first Muslim mayor “has done a very bad job on terrorism” and said Khan “has not been very hospitable” to him.

Khan’s office gave permission for London protesters to fly a 20-foot (6-meter) balloon depicting the U.S. president as a screaming baby near Parliament as part of nationwide demonstrations Friday against Trump’s visit.

Khan noted that other European and American cities had, like London, experienced terrorist attacks.

“And it’s for President Trump to explain why he singled me as the mayor of London out and not the mayors of other cities and leaders of other cities,” he told Sky News.

Some opposition lawmakers called for the British government to cancel Trump’s tea with the queen.

Labour Party lawmaker David Lammy tweeted that Trump “hates that London chose a Muslim mayor. The President is racist. He does not deserve to meet our Queen today #StopTrump.”