Downing Street has put down claims from Boris Johnson after he said he and others had been “taken in” over the EU’s backstop option.
The former Foreign Secretary also warned that Britain was heading for a “spectacular car-crash” if the Government stuck to Theresa May’s plans for Brexit.
The warning came as Mrs May gave one of her most positive forecasts yet for Britain’s future after Brexit, telling the BBC: “I believe that our best days are ahead of us.”
When asked by BBC’s Panorama why she thought Brexit was good for Britain, she said: “It gives the United Kingdom opportunities as an independent and sovereign state to build a better future for all our people."
But, Mr Johnson warned that Britain was “heading full throttle for the ditch with a total write-off of Brexit” unless the Prime Minister’s Chequers plan was dropped.
Mr Johnson warned that the “backstop” arrangement at the Irish border, agreed in December between Mrs May and the European Commission President Jean-Claude Juncker, would leave the UK a “vassal state” of the EU.
In his column for the Daily Telegraph, Mr Johnson claimed that he and others had been "taken in" over the EU's backstop option, having been privately assured at the time that it would never be invoked.
But Number 10 said that Mr Johnson had himself signed up to the joint report agreed by Mrs May and Mr Juncker, including the backstop provision, and had remained in government for a further seven months afterwards.
The Prime Minister's official spokesman said: "Boris Johnson was a member of the cabinet which agreed to the December joint report, including the backstop.
"At the time, he congratulated the Prime Minister for her determination in securing the deal.
"He remained in Government for a full seven months after the joint report was agreed. He was also a member of the cabinet sub-committee which agreed the UK's proposed customs backstop."
Although she is signed up to the principle of a backstop if no better arrangement can be agreed, Mrs May has robustly rejected the version put forward by Brussels, which would see Northern Ireland remain within the EU customs area and effectively draw a customs border down the Irish Sea.
However, Mr Johnson denounced alternative plans set out by the PM as a "constitutional abomination" which would leave Britain as a "humiliated rules-taker".