The DUP have said there will be “major implications” at Stormont if the Foreign Secretary fails to swiftly set a formal deadline to end negotiations with Brussels over the Northern Ireland Protocol.

Days after the EU’s chief negotiator Maros Sefcovic claimed “London has breached a great deal of trust” with Europe over the protocol, DUP leader Sir Jeffrey Donaldson said Liz Truss needed to provide a “clear date” for ending the talks.

“We need a clear date now, we need a clear timeline in which there is an expectation of real progress or the Government takes the action that is necessary,” Sir Jeffrey told The Sunday Telegraph.

“It is crucial that Liz Truss moves this process forward quickly and that we get real and meaningful progress on a range of issues, not least of which is removing the checks on the movement of goods within the United Kingdom internal market.”

Sir Jeffrey would not specify a reasonable deadline for Ms Truss to make progress when asked by the Telegraph, but said: “January is going to be an absolutely crucial month.”

“If we don’t get rapid and decisive progress, and one side or the other is kicking the can down the road, this will have major implications for the stability of the political institutions in Northern Ireland,” Sir Jeffrey added.

European Commission vice president Mr Sefcovic on Thursday told German news website Der Spiegel that problems with the protocol – a way to maintain a free-flowing land border on the island of Ireland after Brexit – meant the UK “broke international law” in trying to get round the arrangement.

Mr Sefcovic told Der Spiegel he is “pragmatic” about Ms Truss taking on responsibility for post-Brexit negotiations with the EU, after Brexit minister Lord Frost resigned last month.

But he warned if Ms Truss was to trigger Article 16, a move that would effectively unilaterally suspend the treaty agreed between the UK and the EU, it would throw into jeopardy “the foundation of the entire deal” reached between the two sides.

Ms Truss has said she remains prepared to invoke Article 16 if issues are not resolved.