Theresa May’s plan to write the date of the UK’s separation from the European Union into law has been dismissed as a “gimmick” and led to fresh warnings it could provoke a Tory revolt as MPs debated the Brexit legislation.

The Prime Minister wants 11pm GMT on March 29, 2019 enshrined in law as the point that the UK breaks away from Brussels.

But as the Commons began its first day of detailed scrutiny of the European Union (Withdrawal) Bill, the move was condemned by Labour and relations within the Tory party were described as “stormy” as a result of the Government’s handling of Brexit.

Countdown to leaving the EU
(PA Graphics)

Meanwhile, Brexit Secretary David Davis sought to reassure businesses that progress was being made in talks with Brussels and said agreement on an implementation period between the date of leaving the European Union and the start of a new trading relationship could be secured “very early next year”.

But the European Parliament’s Brexit co-ordinator Guy Verhofstadt suggested there had been “no progress” in the talks and cast doubt on whether EU leaders would give the green light to move onto the next phase – covering the implementation and future relationship – at a crunch summit next month.

In the Commons, the so-called repeal bill began eight days of detailed scrutiny, with key votes expected later in the process.

How MPs could vote on the EU (withdrawal) bill
(PA Graphics)

Pro-EU Tory Anna Soubry said a private meeting between Conservative MPs and party whips on Monday evening was “stormy”, with critics going beyond the usual potential rebels.

“These are people, a lot of them ex-ministers, highly respected, and they are genuinely cross about this,” she told the BBC.

“There were some people there who have never rebelled and they are now talking, for the first time ever, of rebelling.”

And in further sign of the difficulties faced by the Government – which will be forced to rely on DUP votes for a majority – senior Tories spoke out in the Commons.

Former chancellor Ken Clarke said the amendment on the date was “not just ridiculous and unnecessary – it could be positively harmful to the national interest”.

Ex-attorney general Dominic Grieve said the move was “very strange” and could damage the Government’s negotiating position by limiting the flexibility available to ministers.

Shadow Brexit secretary Sir Keir Starmer said the Government’s bid to write the date of withdrawal into the law was a “desperate gimmick” from the Prime Minister in an effort to keep her party’s Eurosceptics in line.

“The Government’s amendments to their own Bill would stand in the way of an orderly transition and increase the chance of Britain crashing out of Europe without an agreement,” he said.

“Theresa May should stop pandering to the ‘no deal’ enthusiasts in her own party and withdraw these amendments. If not, Labour will vote against them to support our own amendments and guarantee a transition that protects jobs and living standards.”

500 days to Brexit: Key events
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Brexit Secretary Mr Davis addressed financiers following warnings from business leaders that unless an implementation period is agreed by Christmas, firms will increasingly be forced to make arrangements to move work to other EU nations.

Mr Davis acknowledged that investors needed certainty and “without such an implementation period, some of these decisions would need to be taken in the coming January”.

“That is why we want to agree this period as soon as the EU have a mandate to do so. Which I believe can be done, very early next year.”

But Mr Verhofstadt warned that the UK’s offer on citizens’ rights does not go far enough to allow Brussels to conclude that “sufficient progress” has been made in divorce talks at next month’s summit of EU leaders.

In a letter to Mr Davis, obtained by the Associated Press, the Belgian MEP said that “under your proposals EU citizens will definitely notice a deterioration of their status as a result of Brexit”.

Stating that EU citizens in the UK “should notice no difference” in their status after Brexit, Mr Verhofstadt raised concerns over the cost of registration for “settled status”, the requirement to register individually and the risk of deportation.

Any challenge to registration should put the burden of proof on British authorities, not EU citizens, he said.