BORIS Johnson has received a withering put-down from Barack Obama after the London mayor was accused of racism for suggesting the “part-Kenyan” US president harboured an "ancestral dislike" of Britain.

The controversy threatened to overshadow Mr Obama’s three-day visit to Britain after Mr Johnson in a critical article highlighted the way a bust of Winston Churchill had been removed from the Oval Office after the 44th president took office.

"Some,” wrote the Tory MP, “said it was a snub to Britain. Some said it was a symbol of the part-Kenyan president's ancestral dislike of the British empire; of which Churchill had been such a fervent defender."

His remarks caused a political backlash with Labour’s John McDonnell, the shadow chancellor, urging Mr Johnson to withdraw them, tweeting: “Mask slips again. Boris part-Kenyan Obama comment is yet another example of dog-whistle racism from senior Tories."

Scottish peer Lord Campbell, the former Liberal Democrat leader, accused the London mayor of committing an “unacceptable smear” against the president.

During a press conference in the Foreign Office, Mr Obama, clearly stung by Mr Johnson’s comments, took him to task but without referring to him by name.

The president made clear his admiration for the British wartime leader, revealing that he had a bust of him outside the Treaty Room; his private office on the second floor of his official residence.

"Right outside the door of the Treaty Room,” he explained. “So that I see it every day - including on weekends when I'm going into that office to watch a basketball game - the primary image I see is a bust of Winston Churchill.

"It's there voluntarily because I can do anything on the second floor. I love the guy."

The president suggested many Britons would sympathise with the replacement he had chosen for the Oval Office.

"I thought it was appropriate…as the first African American president, it might be appropriate to have a bust of Dr Martin Luther King in my office to remind me of all the hard work of a lot of people, who had somehow allowed me to have the privilege of holding this office.

He added pointedly: "That's just on Winston Churchill. People should know that; know my thinking there."

David Cameron dodged the issue by saying: “Questions for Boris are questions for Boris.”

But Tory MP and Remain supporter Sir Nicholas Soames, Churchill's grandson, did not hold back, saying Mr Johnson’s remarks were "deplorable" and "completely idiotic" and showed Mr Johnson did not have the "stature" to be party leader or prime minister.

The London mayor was forced onto the defensive over his remarks. On a visit to a fast food restaurant in his Uxbridge constituency, he said: "Obviously, people will make of the article what they want."

He went on: "The crucial point is that I'm a big fan of Barack Obama; I was one of the first people to come out in favour of him ages ago.

"But there's a weird paradox when the President of the Unites States, a country that would never dream of sharing its sovereignty over anything, instructs or urges us politely to get more embedded in the EU, which is already making 60 per cent of our laws.

"The issue really is about democracy; America guards its democracy very jealously and I think we should be entitled to do so as well," added Mr Johnson.