Boris Johnson will not have the loyalty of Conservative MPs if he becomes party leader because he is leading a divisive Brexit campaign trumpeting "depressing and awful" arguments on immigration, Sir John Major has said.
The former prime minister described Mr Johnson - widely understood to have ambitions to lead the Tories - as a "court jester" and questioned his "late conversion" to backing Leave.
He warned the former London mayor that he will be treated like ex-party leader Iain Duncan Smith, who was a serial rebel over Europe during Sir John's premiership in the early 1990s.
Sir John said Mr Johnson had the power to stop "fundamentally dishonest" Leave campaign claims on the economy and "squalid" arguments on immigration.
He told BBC1's Andrew Marr Show: "He's a very engaging and charming court jester and a very engaging and charming public figure and he's very likeable and people like him.
"But I think I would offer him this piece of advice - if the Leave campaign led by Boris continue to divide the Conservative Party as they are doing at the present time, and if Boris has the laudable ambition, for it is a laudable ambition, to become prime minister, he will find if he achieves that that he will not have the loyalty of the party he divided.
"Iain Duncan Smith was serially disloyal in the 1990s, when he became leader he was surprised that no one was loyal to him and Boris should learn from that.
"I think Boris, all his instincts of the past have been of a one nation Tory, which is where I stand, he seems to have drifted away from that with the way in which they are approaching immigration and some of the other things.
"I'd like to see him get back, because if he gets back he is an important, engaging Conservative figure."