Boris Johnson is digging his own political grave after comparing Theresa May's Brexit plan to a suicide vest, his former aide has said.
Ex-foreign secretary Mr Johnson claimed Mrs May had "wrapped a suicide vest" around the British constitution and "handed the detonator" to Brussels.
He quit his role this summer in protest at Mrs May's Chequers deal on how the UK would leave the EU in March 2019.
But former aide Guto Harri, warned he is damaging himself and the country.
"I fear Boris is digging," said Mr Harri, who was Mr Johnson's communications director when he was Mayor of London, told BBC Radio 4's The Week In Westminster.
"Somebody needs to take the spade out of his hand. It looks to me like he's digging his political grave.
"It's one to deploy humour and charm and intellect and all these things he has in spades, which he has done brilliantly in the past... but at the moment it is being deployed in a really destructive and self destructive way that is doing enormous damage to him as well as to the country.
"What I regret now is he is deploying that talent without a plan."
Mr Johnson, a prominent Leave campaigner has been at odds with Mrs May's vision for Brexit for some time and has spoken out against her several times.
He has said the PM's plan would hand the EU "victory" in Brexit negotiations.
Mrs May's plan would see the UK agreeing a "common rulebook" with the EU for trading in goods, in an attempt to maintain frictionless trade at the border.
Critics argue this would leave the UK tied to EU rules after it leaves on 29 March 2019, and prevent Britain from striking its own trade deals in years to come.
If the UK and the EU do reach a deal, MPs will then have to approve it.
But Mr Harri, from Cardiff, believes Mr Johnson has damaged any hopes of becoming prime minister in the future.
"Over a period of time Boris did move from celebrity to statesman and did widen his appeal enormously," he said.
'Become more tribal'
"He was a huge unifying figure by the end of my time with him, when the Olympics happened in London, there were people on the left and right. Now he's gone other other way.
"He's become more tribal and tribal within the tribe. So that he would now be, if he were to become leader, be a hugely divisive figure.
"Unfortunately he's now dragging us to a place where we can joke about suicide vests.
"The very nature of a suicide vest is you blow yourself up which is why it is an appropriate analogy for Boris only he's mis-directed the analogy by saying the trigger is in someone else's hand. It's in his."
"The tragedy for me is that he could have been prime minister."
But Andrew Gimson from Conservative Home blog does not think it is the last chance for Mr Johnson to become PM.
"He's a disruptor and that's how he cheers people up," he said,
"That is actually what a lot of people, who live a long way from London, want.
"They feel that we've dithered, we've been very feeble and they want someone who's actually prepared to be rude to people and including the people in Brussels.
"Liberal Boris is still there."
Mr Johnson has been asked to comment.