Former British Foreign Secretary Boris Johnson walks on Downing Street in London on March 7, 2018. (Photo: VCG)

Former British Foreign Secretary Boris Johnson on Sunday flayed Prime Minister Theresa May's Brexit plan, calling it a "suicide vest" around the British Constitution with the detonator handed to the European Union's Brexit negotiator Michel Barnier.

The criticism came in an article Johnson wrote for The Mail on Sunday, where he said the deal, struck at Chequers, the official country residence of the prime minister, had opened Britain to perpetual political blackmail.

Johnson quit his job in July, following the cabinet agreeing to the plan.

Johnson's comments were criticized by some conservative MPs, who supported the prime minister.

Foreign Secretary Jeremy Hunt wrote in the same paper that the country should back May and her plan.