Sir Jeffrey Donaldson

The DUP negotiator warned Leo Varadkar last night that the agreement required Northern Ireland to determine its own future without external interference.

Mr Varadkar said yesterday that UK and Irish ministers should use an intergovernmental peace process body to plot a way forward for Northern Ireland if devolution is not restored as a result of ongoing talks.

Leo Varadkar reiterated that Dublin would not accept direct rule but would urge the recall of the British Irish Inter-Governmental Conference (BIIGC) if a deal to revive power-sharing proved elusive.

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But Lagan Valley DUP MP Mr Donaldson hit back: “We have made it clear to the prime minister and secretary of state that this is fundamentally unacceptable.”

Mr Donaldson added: “Under the Good Friday Agreement (GFA) the Irish government is forbidden to interfere in the internal matters in Northern Ireland.

“If the Irish government proceeds down this path it will cross the line and this will have very serious consequences for the restoration of political instututions.”

Mr Varadkar’s proposal was also “a fundamental breach” of the GFA’s three strand approach to Northern Ireland, which requires a Belfast assembly as well as north-south and east west dimensions, he said.

It was also a breach of the principal of consent, whereby NI cannot be brought into a united Ireland without majority support.

Mr Varadkar had called for the recall of the bilateral body, a construct of the 1998 GFA, which brings together UK and Irish ministers to encourage cooperation on matters of mutual interest.

It last met in 2007.

Mr Varadkar said his government was opposed to a return to Westminster direct rule as it existed pre-1998.

While Sinn Fein has been calling for a greater Irish role in resolving the impasse, DUP leader Arlene Foster has dismissed the British-Irish Inter-Governmental Conference as a “talking shop”.

Sinn Fein’s Pearse Doherty asked Mr Varadkar about the conference during exchanges in the Dail yesterday.

The Taoiseach said he had met Theresa May on Friday. “As I have done at previous meetings, I said to Prime Minister May that the Irish government could not accept a return to direct rule as it existed prior to the GFA and that if Sinn Fein and the DUP failed to form an administration, the government I lead would expect the Good Friday Agreement to be implemented without them.

“That means convening the BIIGC, as if nothing is devolved then everything is devolved to that conference.

“I indicated to her I would seek a meeting in the new year of the BIIGC so British and Irish ministers could meet to plot a way forward for Northern Ireland in the absence of the elected representatives in NI being able to form an administration.”

Also yesterday, DUP leader Arlene Foster hit back at comments from Mr Varadkar that a hard border should be off the table. The DUP leader warned against “playing about with Northern Ireland”.

Asked to clarify what she meant when she said that Brussels was “using Northern Ireland as a bargaining chip”, Mrs Foster told the BBC’s Laura Kuenssberg: “Particularly the Irish government, in the way they are referring to Northern Ireland in the negotiations around the border.”

Asked if she was accusing the Irish government of being reckless, Mrs Foster said: “I am accusing them of being reckless because if you listen to some of the rhetoric – and look, nobody understands negotiations probably better than I – there are people who will come out and say things to try and push agendas forward.

“We do recognise that we are at a critical phase because we all, well certainly I, want to see the negotiations move to the second phase so that we can talk about those issues of trade, and the issues that will make a difference, actually, to the border between Northern Ireland and the Republic of Ireland.

“It’s almost a faux battle because, actually, the detailed issues will come about when we are talking about the trade issues.”