The Government has been accused of presiding over a Brexit “shambles” after the minister leading negotiations was forced into an embarrassing climbdown, while officials highlighted major flaws in the UK’s withdrawal plans.

Brexit Secretary David Davis performed a same-day U-turn after angering Downing Street by claiming the House of Commons may not get to approve any Brexit deal until after the country has left the EU.

In a difficult day for Theresa May, the UK’s ex-ambassador to Brussels also suggested her approach could leave Britain “screwed” in negotiations, while HMRC could not say border systems will be ready in time for a “no deal” Brexit.

Ex-attorney general Dominic Grieve, leading attempts to reshape the PM’s Brexit plans, later said Britain may have to extend its EU membership beyond March 2019 to allow time for a final deal to be properly ratified by Parliament.

The Government’s troubles began when Mr Davis bragged at a 9.15am Brexit Committee hearing that negotiations will drag on until the last minute and be “very exciting”.

Asked if that meant the promised Parliamentary vote on the agreement could be delayed until after Brexit Day, in March 2019, Mr Davis replied: “Yes, it could be”.

With Ms May already under pressure from Tory backbenchers to allow Parliament a greater say over her Brexit deal, she attempted during Prime Minister’s Questions at noon to correct Mr Davis by saying she was “confident” a vote could take place ahead of the 2019 deadline.

Brexit: the deciders Show all 8 1 /8 Brexit: the deciders Brexit: the deciders European Union's chief Brexit negotiator, Michel Barnier Getty Brexit: the deciders French President Emmanuel Macron Getty Brexit: the deciders German Chancellor Angela Merkel Reuters Brexit: the deciders Commission President Jean-Claude Juncker EPA Brexit: the deciders The European Parliament's chief Brexit negotiator Guy Verhofstadt Getty Brexit: the deciders Britain's Prime Minister Theresa May Getty Images Brexit: the deciders Britain's Chancellor of the Exchequer, Philip Hammond PA Brexit: the deciders After the first and second appointed Brexit secretaries resigned (David Davis and Dominic Raab respectively), Stephen Barclay is currently heading up the position PA

But her words, falling short of guarantee the vote would happen, failed to quell anger leaving Labour MPs demanding a statement in the House and Tory backbenchers grumbling about Mr Davis’ competence.

By 4pm his department issued a statement explaining that Mr Davis’s morning words had been dealing with “hypothetical scenarios” and that he did indeed expect a vote in the Commons before the UK left the EU.

The Independent understands that Ms May had been angry at having to fire-fight problems created by Mr Davis as she prepared for her weekly PMQs session.

Her spokesman later did not deny Downing Street had been in contact with Mr Davis department before it published its clarification of his comments, and was also forced to say that Ms May still has “confidence” in his abilities.

Speaking to The Independent afterwards, Conservative MP Nicky Morgan said: “I hope he’ll stop asking himself hypothetical questions as we’ve got enough really hard questions to answer.”

Labour’s Sir Keir Starmer refuted Mr Davis’s words (Getty)

Ex-business Tory minister Anna Soubry said Mr Davis’s comments had been “really worrying”, adding: “Any eleventh hour deal is going to be in the run up to the end of next year, not March 2019, because it needs to be ratified by other European parliaments. He must know that, he’s the secretary of state.”

Jeremy Corbyn’s spokesman said Mr Davis words were “obviously absurd”, while Shadow Brexit Secretary Sir Keri Starmer said no one in any other European country or in Brussels had suggested ratification would come after March 2019.

Labour Pat McFadden MP, leading supporter of Open Britain, said the U-turn exposed the “self-created shambles” over Brexit, while the Lib Dems Tom Brake said it showed the “total contempt” with which the Government holds Parliament.

As Downing Street was managing the fallout, the UK’s former ambassador to the EU said Ms May’s decision to trigger Article 50 without first establishing the sequencing of talks had opened up Britain to being “screwed” in negotiations.

Giving evidence to the Treasury Committee, Sir Ivan Rogers said he advised waiting until ministers were sure how the negotiating timetable would work but said he had been “heavily opposed” by “various people in London”.

At the same time in a hearing of the Public Accounts Committee, the chief executive of HM Revenue and Customs said there is no “guarantee” a new IT system will be ready for a no-deal Brexit.

Mr Davis did receive some support from hardline Brexiteer MPs, including Chris Chope who said Mr Davis had made a “perfectly sensible point”, suggesting that a deal may be pushed to the last minute and that therefore Parliament will not vote until afterwards.

Theresa May refuses to guarantee MPs vote on Brexit deal before Britain leaves EU

Mr Chope was himself sitting on the Procedure Committee questioning Mr Grieve about his proposed amendment to the Government’s EU (withdrawal) Bill, that would see it committing to a enshrine the eventual deal Ms May seals in UK law with a new piece of legislation.

Mr Grieve said Britain may have to temporarily extend its EU membership if a Brexit deal has not been ratified by both sides at the planned exit date of March 2019.

He explained: “What will happen is that there will be a necessary extension, short extension, of time on both sides for this matter to be resolved.”