Even before he sets foot in Britain on Monday at the start of his three-day state visit to Britain, President Donald Trump has breached diplomatic protocol by appearing to endorse Boris Johnson in the battle to replace Theresa May as the country’s next Prime Minister.

The President told The Sun newspaper in a 20-minute exclusive interview in the Oval Office the White House in Washington: “It’s something (the choice of PM) that I find very interesting. I actually have studied it very hard. I know the different players. But I think Boris would do a very good job. I think he would be excellent.”

Trump, 72, also insisted that Boris’s well-known philandering scandals should not halt him from winning, according to The Sun.

Asked whether he thought Boris’s extra-marital affairs and love child mattered, the President replied: “Well, it always matters, but I think that it’s certainly not what it was 20 years ago, and not certainly what it was 50 years ago. I think today it matters much less.”

The President added: “I like him. I have always liked him. I don’t know that he is going to be chosen, but I think he is a very good guy, a very talented person. He has been very positive about me and our country.”

The report by the paper’s political editor, Tom Newton Dunn, went on: “In more explosive remarks, he also claimed that he could have a big impact on the race for No10 — currently being fought by 12 different candidates. And he claimed that several other contenders had also approached him. “He said: ‘Other people have asked me for an endorsement too. I have been asked for endorsements.’

“Quizzed on who, Trump replied: “Well, I don’t want to say who but other people have asked me for endorsements, yes.’” He added: “I could help anybody if I endorse them. I mean, we’ve had endorsement where they have gone up for forty, fifty points at a shot. Now that is here (in the US), but I understand over there would be a great endorsement.’ ”

Opinion was divided on Saturday whether Trump’s comments will actually affect Boris’s chances. The received wisdom seems to be that they will probably cut both ways since Trump himself is a controversial character.

The President also revealed to The Sun that he looks favourably on Jeremy Hunt too, saying of the foreign secretary: “Yup. Like him.”

Trump was critical of May’s negotiating tactics when seeking a good Brexit deal from the EU: “I think that the UK allowed the European Union to have all the cards. And it is very hard to play well when one side has all the advantage.

“I had mentioned to Theresa that you have got to build up your ammunition. I am sure that you could have built up a big advantage for your side and negotiated from strength.

“You have to build up your side in terms of points, or you are just going in and asking, I mean it was just asking and you know, they would say whatever they wanted.”

“They had nothing to lose. They didn’t give the EU anything to lose. At the same time, I respect Theresa and she would certainly know the facts a lot better than I know them.”

Trump was also asked about Meghan, Duchess of Sussex, who will stay at home with her baby and not attend the state banquet which Prince Harry will.

The President said he was surprised Meghan was “nasty” about him but that it was great to have an “American princess”.

Despite the huge protests being planned Trump insisted: “I am really loved in the UK.”