Brussels said the Withdrawal Agreement must be effectively implemented – and cautioned that respecting legal obligations would be “very important” for establishing trust between the UK and EU in future negotiations.

Dana Spinant, deputy chief spokeswoman of the European Commission, told reporters at a briefing: “The Withdrawal Agreement has been signed and ratified by both sides and as such it must be effectively implemented.

“That includes, of course, the protocol on Northern Ireland and all its constituent parts.

“Of course, in this context as in all others, we would expect our partners to respect their international obligations under their national law and under international law – that includes, of course, the Withdrawal Agreement which has legal force.

“Obviously, with respect to the future and how this plays in the negotiation, of course respecting our legal obligations is very important for establishing trust between two partners in a negotiation.” 

Downing Street insisted the UK would “comply with our obligations” under the deal struck with Brussels and said it would require only “limited changes” to Great Britain-Northern Ireland trade.

“The protocol specifically allows the UK to ensure unfettered market access for goods moving from Northern Ireland to GB,” the Prime Minister’s official spokesman said.

“The UK signed the Withdrawal Agreement including the protocol last month, we will comply with our obligations.”

The spokesman added that Boris Johnson “has been clear that beyond the limited changes which are introduced by the protocol, there will be no changes to GB/NI trade”.

“We have not asked any ports to prepare for new checks or controls between GB/NI.”

Downing Street rejected the suggestion from France that the December 31 deadline for a trade deal was an attempt to “blackmail” the European Union into striking a deal at all costs by that date.

The Prime Minister’s official spokesman said: “The UK’s primary objective in the negotiations is to ensure that we restore our economic and political independence on January 1 2021.”