BORIS Johnson has delivered a devastating critique of Theresa May’s Brexit policy in his resignation letter, saying the dream of the UK leaving the EU is “dying” in her hands.

The former Foreign Secretary said the country would be reduced to a “colony” of Europe if it followed the Prime Minister’s plan for a soft Brexit.

The leading figure of the Vote Leave campaign in 2016, Mr Johnson said voters were told they would regain control of immigration, money, and law-making.

He said: “Brexit should be about opportunity and hope. It should be a chance to do things differently, to be more nimble and dynamic, and to maximise the particular advantages of the UK as an open, outward-looking global economy.

“That dream is dying, suffocated by needless self-doubt.”

Mr Johnson said the Brexit process had been beset by delay and “crucial decisions” postponed, including preparations for a no deal, leaving large parts of the UK economy still “locked in the EU system, but with no UK control over that system”.

He also said the UK was now in the “ludicrous position” of signing up to huge amounts of EU law, “without changing an iota”, on the grounds it was necessary for the economy.

He said: “in that respect we are truly headed for the status of colony - and many will struggle to see the economic or political advantages of that particular arrangement.”

He said that by “surrendering” control over rules for goods and agriculture, it would be “much more difficult to do free trade deals”, while the UK would be arguing “for an impractical and undeliverable customs arrangement unlike any other in existence”.

He said what was more disturbing was this was merely an “opening bid”, before the EU 27 had made their counter-offer.

“It is as though we are sending our vanguard into battle with the white flags fluttering above them,” he wrote.

He said that, after losing the arguments at Chequers on Friday, the cabinet had agreed a position and at least now had “a song to sing”.

But he added: “The trouble is that I have practised the words over the weekend and find that they stick in the throat.

“We must have collective responsibility. Since I cannot in all conscience champion these proposals, I shave sadly concluded that I must go.”

The statement emerged three hours after Downing Street tried to spike Mr Johnson’s guns by announcing his resignation first, while he was still drafting the letter.