The UK has already drafted legislation to put any Brexit deal it strikes with the EU into law, HuffPost UK has learnt.

A 50-page “draft future relationship bill” is in existence with time running out until the end of the transition period on December 31.

HuffPost UK understands that the current text forms a skeleton to which the details of any last-minute UK-EU trade agreement can be added.

MPs were on Thursday sent home for the Commons’ Christmas recess, but put on notice that they could be recalled before January to approve any deal Boris Johnson strikes with the EU.

A failure to strike a deal by December 31 would see the UK default to World Trade Organisation (WTO) terms for trading with the EU from the next day, which is predicted to be the most damaging outcome.

Earlier this week, Commons leader Jacob Rees-Mogg said it could take six days to put a Brexit deal struck at the negotiating table into UK law.

He reportedly told the Moggcast, hosted by Conservative Home: “If there were an agreement today I think you would need six days in that you would have the text tomorrow, you would have 48 hours to write the bill and you would have a day in the Commons, a day in the Lords and a day for Royal Assent.”

The draft legislation forms part of the government’s contingency planning, which could see MPs sitting in the Commons on New Year’s Eve to ratify a last-minute Brexit trade bill.

One option is to bring any Brexit trade treaty before the Commons for a fast-tracked one-day approval on December 28, with the House of Lords told to get ready for a two-day scrutiny period on December 29 and 30.

The Commons would then complete the process on December 31, just hours before the UK leaves the “transition period” – under which it has operated within EU rules since formally leaving the bloc last January. 

The European Parliament has meanwhile set down a three-day deadline for post-Brexit trade deal negotiators to strike a deal, warning that MEPs will not have time to ratify an agreement this year unless it is ready by Sunday night.

Presidents of the parliament’s political groups said it was ready to organise a plenary session by the end of the month, but on condition that “an agreement is reached by midnight on Sunday December 20”.

But it is understood that the EU could choose to apply any deal provisionally and then seek the approval of MEPs later.

On Thursday, the UK and EU gave contrasting assessments of the chances of agreement, with Michael Gove suggesting it was “more likely” there would be no deal.

Despite a sense of optimism in recent days, Gove said the chances of a deal are now “less than 50%”.

The Cabinet Office minister also said the “most likely outcome” was that the current transition period would end on December 31 without a deal.

“I think, regrettably, the chances are more likely that we won’t secure an agreement. So at the moment less than 50%,” he told the Commons Brexit committee.

But he appeared at odds with EU chief negotiator Michel Barnier, who described “good progress” in the talks with his opposite number from the UK, Lord Frost, while acknowledging the “last stumbling blocks remain”.

Barnier briefed European Parliament leaders about the state of the talks, which he said were in the “final stretch”.

He said: “We will only sign a deal protecting EU interests and principles.”