Britain's chief Brexit negotiator predicted that the UK would have to give into EU demands if it wanted a trade deal, it has been revealed.

In a forgotten pamphlet written just before the 2016 referendum, Lord Frost argued that “it will be Britain that has to make the concessions to get the deal”.

It comes amid reports that the European Parliament could hold a key vote on any Brexit agreement just days before Britain is set to crash out of the single market on 31 December.

The Guardian newspaper says parliament officials are considering holding the vote on 28 December to give both sides more time to prolong negotiations.

Britain and the EU are stretching a mid-November deadline to conclude talks, which both sides said was the last moment a free trade agreement could be agreed in time for the end of the year.

But a 28 December vote in Brussels could see officials work through Christmas to prepare a treaty - which is still far from certain to be agreed.

Given the tight deadlines, Boris Johnson has been urged to write an "adjustment period" into any Brexit trade deal to give businesses breathing space.

Lib Dem leader Sir Ed Davey and former Siemens boss Juergen Maier said: "Uncertainty is bad for business at any time, but the combination of the challenges of battling the impact of coronavirus restrictions alongside having now to cope with the huge challenge of complying with new trading procedures, at very short notice, could be very damaging.

"Indeed, some in the business community tell us they are seriously concerned that the threat they face due to these twin challenges is existential. Industry bodies from every sector of the economy have warned that they will need time to adjust.

"So we urge you to negotiate the reasonable and practical measure of a three to six-month adjustment period in the EU trade deal, to save jobs and businesses.

"By phasing in new rules, regulations and procedures, our businesses would have the breathing space they need to prepare and adapt. The UK will also have time to prepare for the logistical burden of customs checks at the border."

Lord Frost's 2016 report, unearthed by the Financial Times, was written in a personal capacity by the future negotiator and published by political consultancy and PR agency Portland Communications.

The document, entitled “Britain Votes Leave: What Happens Next”, also argued that it "simply isn’t worth jeopardising access to the single market for the sake of global trade". This is now explicit UK government policy.

Despite Lord Frost's previous suggestion that Britain would have to make concessions, the UK has so far in talks claimed the opposite is true, arguing that it has fundamental principles to which the EU must adjust if it wants a deal.