The front-runner to become Britain’s next prime minister is a portly white man with unkempt blond hair, an adoring base of supporters, disdain for Europe, a dodgy private life and a loose relationship with truth and principle. There are also differences between Boris Johnson and Donald Trump, but the similarities have been much noted in some European circles, with no small misgivings.

The biggest difference is that Mr. Johnson, who is 55, has been around politics all his life, as a journalist, member of Parliament, mayor of London and foreign secretary. His forte has not been conservative conviction, major achievement or great vision, but one of the sharpest tongues in British politics.

Like Mr. Trump with his tweets and rants, Mr. Johnson delights his followers with outrageous statements that they take as straight talk — even when he has gone so far as to describe Africans as “piccaninnies” or to ascribe President Barack Obama’s opposition to Brexit to an “ancestral dislike” of Britain as the son of a Kenyan.

His most commonly quoted quip these days is the one summing up his position on Brexit as having one’s cake and eating it. Curiously, Mr. Johnson was initially unsure of his position on leaving or remaining in the European Union — an unpublished article he wrote days before he came out in favor of leaving made a strong argument in favor of staying. Mr. Johnson says he was simply sorting out his thoughts.