Boris Johnson is “digging his political grave” with a series of ill-judged remarks and would be “hugely divisive” as prime minister, according to a key former aide.

Guto Harri, communications director for four years while Johnson was mayor of London, told the BBC’s Week in Westminster program Saturday that his former boss had gone from being a unifying politician who could use wit and charm to span the left-right political divide, to a far more tribalistic figure.

Johnson resigned as foreign secretary in July in protest at Theresa May’s Brexit plans, and is now seen as the front-runner to replace her because of his popularity with Tory grassroots members.

“Unfortunately he is now dragging us into a place where we think that we can joke about suicide vests and that we can be sexually incontinent,” said Harri, referring to a column in which Johnson compared May’s negotiating stance to putting a “suicide vest” around the British constitution, and to reports of Johnson’s numerous alleged affairs.

“Somebody needs to take the spade out of his hand or it looks to me like he’s digging his political grave,” said Harri, who has not spoken publicly before about his former boss.

“He was a huge unifying figure by the end of my time with him when the Olympics happened in London,” he said. “He would not have been re-elected in a left-leaning city like London if he hadn’t appealed to the left.”

“Now he’s gone the other way. He’s become more tribal, and tribal within the tribe, so that he would now be — if he were to become leader — a hugely divisive figure.”

Speaking to the same program, former Deputy Prime Minister Michael Heseltine said he could not see a Tory leadership contest scenario in which Johnson was not placed in the top two in a ballot among Tory MPs. Those contenders would then run-off in a poll of party members.

“If he gets before the activists, my guess is that he will get the nomination,” said Heseltine.