Mitt Romney has been rebuked by the US Olympic legend Carl Lewis after the presumptive Republican presidential nominee questioned whether London was fully prepared for the Olympic Games.

As Romney was mocked on US television and by the London mayor, Boris Johnson, in front of a crowd of 60,000 people, Lewis called on him to return home.

“Seriously, some Americans just shouldn’t leave the country,” the nine-times Olympic gold medal winner told the Independent.

Asked whether London was ready to stage the Games, Lewis said: “Of course London is ready.”

Romney stumbled into a diplomatic disaster on the first stage of his first official overseas visit as the presumptive Republican nominee when he told NBC there were “disconcerting” signs that London was ill-prepared for the Olympics.