Conservative MP Boris Johnson speaks as he visits Bristol on May 14, 2016 in Bristol, England.

Prime Minister Theresa May's Brexit deal wraps "a suicide vest around the British constitution" and hands the detonator to the European Union, former foreign secretary Boris Johnson said in comments that drew strong criticism.

In an article in the Mail on Sunday newspaper, Johnson pressed his attack on May's so-called Chequers plan to leave the EU, calling it "a humiliation" that opens "ourselves to perpetual political blackmail".

May is under fire from all sides of the divisive Brexit debate, with Johnson, favorite to succeed her, leading a push by euroskeptic MPs for the government to "chuck Chequers" and pursue a clean break with the bloc.

But so far, May has signaled she will not drop her blueprint for Britain's future ties with the bloc after Brexit — the biggest shift in the country's foreign and trade policy for almost half a century.

"We have wrapped a suicide vest around the British constitution — and handed the detonator to (EU chief negotiator) Michel Barnier," Johnson wrote.

His words — particularly the reference to a suicide vest — drew condemnation from fellow members of the governing Conservative Party.

Alan Duncan, a minister at the Foreign Office, said Johnson's comments marked "one of the most disgusting moments in modern British politics".

"For Boris to say that the PM's view is like that of a suicide bomber is too much," he said on Twitter. "I'm sorry, but this is the political end of Boris Johnson. If it isn't now, I will make sure it is later."

Cricket - England v India - Fifth Test - Kia Oval, London, Britain - September 8, 2018 Boris Johnson in the stands Action Images via Reuters/Paul Childs