Boris Johnson’s treatment at the hands of Luxembourg’s prime minister is a reminder of why the UK wants to leave the European Union, the US ambassador said on Tuesday night.

In a show of solidarity, Woody Johnson said that having “built the greatest empire” and “held off the Nazis”, the British “didn’t need a lecture from anybody on how to run their country ... and that includes Brussels”.

He added: “We stand with the people of the UK and we always will.”

It came after Xavier Bettel, the Luxembourg prime minister, was accused of “disrespecting” Britain after he tried to force Mr Johnson to hold a news conference in a street full of anti-Brexit protesters, leaving the Prime Minister no choice but to pull out.

Speaking at the Carlton Club on Tuesday, the US ambassador praised Mr Johnson’s handling of the situation, insisting that “he knew he was walking into a trap”. “He knew this was a set up. Of course he knew, but he’s British. He said: ‘What the hell. I can do this’.