Prime minister Boris Johnson is “fascinated” by Donald Trump and is intrigued by his American counterpart's patchy relationship "with the facts and the truth”, according to a former British ambassador to the US.

Lord Kim Darroch makes the claim in a new book, serialised in The Times, where he suggests Mr Trump had also considered Mr Johnson "a kindred spirit".

Mr Johnson had allegedly been "fascinated" by the president on visits to Washington as foreign secretary before he became prime minister, with particular focus on Mr Trump’s use of language.

This includes "the limited vocabulary, the simplicity of the messaging, the disdain for political correctness, the sometimes incendiary imagery, and the at best intermittent relationship with facts and the truth", Lord Kim writes.

In an interview accompanying the excerpts, Lord Kim was asked if any of those characteristics had rubbed off on Mr Johnson.

"From what I hear from colleagues," he replied, "this government pays a lot of attention to presentation, to language.

"But if you go back through the current prime minister's history, he's often said quite striking things. And he never apologises.

"So, Boris might have done this anyway, but certainly, having watched Trump in action, he wouldn't have been put off."

Lord Kim also says he told Mr Johnson he was partly to blame for his resignation from his Washington post, following the leaking of a cable in which the ambassador said Mr Trump was "inept" as president.

Mr Johnson, who was then running for the Conservative leadership, repeatedly refused to say he would keep him in the post during a TV debate on 9 July last year.

Lord Kim resigned the next day and spoke with Mr Johnson by phone.

"He said: 'But why did you resign? Wouldn't it all have blown over after a few weeks?"' Lord Kim told The Times.

In answer to Mr Johnson's question as to whether the resignation was his fault, Lord Kim told him that "in part it was".

After Lord Kim left the diplomatic corps following a distinguished 42-year career, Mr Trump fired back with a range of epithets, calling him "the wacky ambassador", "pompous", and "a very stupid guy".

Former US national security advisor John Bolton has meanwhile claimed that Mr Trump demanded the removal of Lord Kim from his position.

“Trump called me and said ‘get him out of here’,” Mr Bolton told The Daily Telegraph. “I mean at like seven in the morning or six in the morning. Early. I was at the office but even for Trump that was early.”

In a subsequent phone call with Sir Mark Sedwill, then the UK’s top civil servant, Mr Bolton told him: “Things are going to get worse unless you can figure out how to get him out”.