Theresa May has again slammed the brakes on the Brexit bill, as a growing Tory backbench revolt threatens to force her into another embarrassing U-turn.

Crunch votes – including on the Prime Minister’s controversial pledge to put the precise date of EU withdrawal in domestic law – could be shelved until after Christmas.

The move prompted a suggestion from the pro-EU campaign group Open Britain that the Government may be preparing further concessions.

“MPs across all parties must have the necessary time to amend it and prevent the chaos of a cliff-edge Brexit,” said Chris Leslie, a Labour MP and supporter of the group.

And Tom Brake, the Liberal Democrat Brexit spokesman, said: “Ministers clearly didn’t anticipate how difficult this Bill would be and thought that they could strip Parliament of its power without any opposition.”

Line-by-line scrutiny of the EU (Withdrawal) Bill was due to be completed next month, with the clock ticking on legal preparations for departure day in March 2019.

But, asked to guarantee that its committee stage would finish by Christmas, Commons Leader Andrea Leadsom told MPs it was “difficult to project forward with absolute certainty”.

Any fresh delay could be seen as an attempt to avoid any shows of weakness before a make-or-break summit of EU heads of state on 14 December.

The Prime Minister’s future could rest on agreement to finally move the Brexit negotiations onto future trade and a transitional period, to avoid a damaging “cliff edge” for businesses, in 2019.

However, under the original timetable, up to 20 Tory backbenchers were poised to rebel on the issue of the exact Brexit date on the eve of that summit.

They fear putting the date – 11pm on 29 March, 2019 – on the statute book will make it impossible for Parliament to force a delay, to prevent a no-deal exit, if no agreement can be reached.

The scale of the revolt could force Ms May to drop the plan, announced just six days ago to calm tensions with pro-Brexit Tories.

Significantly, the potential rebels are the same Conservative MPs who forced the Government to agree to separate – amendable – legislation to implement any exit agreement, in Monday’s climbdown.

Later, Justice Secretary David Lidington hinted at a U-turn over the Brexit date controversy, telling Westminster journalists: "Obviously we will listen to ideas coming from colleagues across the House during the Bill's progress.”

However, further delay would make it impossible for the bill to pass by next spring, the Government’s original timetable.

It will also be mauled in the Lords, where peers will demand changes on so-called “Henry VIII powers” – bypassing Parliament – devolution and the future role of the European Court of Justice.

The bill will be have its third day in committee next Tuesday, Ms Leadsom announced, with a further five to come.

However, she said there was no “absolute certainty” about the future timetable, adding: “We will continue to update the House in the usual way.”

On Tuesday, Dominic Grieve, the former Conservative Attorney General, will lead a challenge to the Government’s refusal to incorporate the EU’s Charter of Fundamental Rights into UK law.

Critics say people will be unable to sue if their rights are infringed – but ministers insist they will be protected in domestic law.