Conservative MPs in the European Research Group were becoming “anxious” on Thursday afternoon at the Government’s delay in publishing the full legal text, according to sources within the group.

There are now five days to go until the Brexit transition period must, by law, end at 11pm on December 31. Mr Johnson has confirmed his plan to push the legislation, which gives legal effect to the trade deal, through both the Commons and Lords in a single day next Wednesday.

However, Mark Francois, chairman of the ERG, told The Telegraph: “It seems incongruous that Parliament should have to ratify what is, after all, an international treaty at breakneck speed next week if the European Parliament can now do so at their leisure until the end of February.”

He said this disparity between the time offered to the two sides’ parliamentarians was “made worse” by the fact the legal text was still not available for pro-Leave legal experts to pore over in the UK. The draft treaty and associated Brexit agreements stretch to 1,246 pages of legal text.

Andrew Bridgen, Conservative MP for North West Leicestershire, meanwhile called outright for the Prime Minister to rethink the plan for MPs to be recalled next Wednesday to rush through the legislation.

He suggested the trade deal could be provisionally applied to avoid a “no-deal” cliff edge on January 1, but insisted MPs be granted time to examine and debate the agreement before formally having their say.

“I would prefer a provisional vote this week so the treaty can start on the December 31 at 11pm, and then both our Parliament and the EU Parliament had several weeks to study and debate, followed by a confirmatory vote,” he said. “Because a Treaty is for decades, not just for Christmas.”

His suggestion mirrors a plan in place for the EU to process the deal. MEPs have already declared that there is not enough time to discuss and ratify such a complex agreement before the end of the year.

In coming days the leaders of the EU 27 member states will therefore ratify and “provisionally apply” the deal until the EU Parliament votes on it later in January.

On Christmas Day morning EU Ambassadors met in Brussels to be briefed on the contents of the deal by Michel Barnier, the EU's chief negotiator.

European officials meanwhile worked through the day to prepare legal documentation.

Earlier this week the ERG, which boasts a membership of about 70 MPs, announced that they would reconvene a panel of lawyers to scrutinise the UK-EU agreement.

The so-called “Star Chamber” of legal experts was first assembled to review Theresa May’s Withdrawal Agreement in March last year.

Sir William Cash, a qualified solicitor as well as the MP for Stone, will resume the chairmanship. His views are held in esteem by ERG colleagues, with some privately warning that Mr Johnson’s deal must pass the “Bill Cash test” if they are to back it.

In a joint statement, Mr Francois and David Jones, deputy chairman of the group, urged Downing Street to publish the legal text of any agreement “as soon as possible”.

Acknowledging that the deal would be “highly complex”, they said: “The Star Chamber will scrutinise it in detail, to ensure that its provisions genuinely protect the sovereignty of the United Kingdom, after we exit the transition period at the end of this year.

“It is intended that the Star Chamber, which will include some amended members (as some previous participants now serve in Government), will undertake its examination as expeditiously as possible, before providing its conclusions on the merits of the deal, which we will aim to make public before Parliament reconvenes.”

Tory MP Sir John Redwood, another veteran Eurosceptic, also ratcheted up pressure on Mr Johnson over the deal, warning on Twitter: “Any UK/EU Agreement must put us in full control of our laws, and needs an exit clause we can use without EU permission.”

Under the terms of the agreement, a formal review of the system can only take place after four years. At that juncture, if the UK or EU does not believe the system is working, they can nullify the deal and trade on World Trade Organisation terms.

The Brexiteers’ “Star Chamber” was named after the court that sat in the Old Palace of Westminster between the fifteenth and seventeenth centuries. Composed of judges and privy councillors, it grew out of the medieval king’s council as an addition to the common-law courts.

The current “Star Chamber” convened in March last year to pore over Mrs May’s withdrawal deal, and was made up of eight MPs from across the Conservatives and Democratic Unionist Party. These included Dominic Raab, now the Foreign Secretary, and Suella Braverman, currently Attorney General.

Sir Bill delivered a blow to Mrs May when, after scrutinising the legal meaning of her deal, he concluded he could not support it.

The panel also publicly questioned her right to delay the UK's planned exit from the EU beyond the original departure date of March 29.