Liz Truss will stand down as Prime Minister within a week meaning there will not be enough time to prevent an Assembly election in Northern Ireland.
A Northern Ireland Office source has told UTV's Political Editor Tracey Magee: "That's the way it is at the minute."
An NIO spokesperson added: "The secretary of state's focus remains on the restoration of the Executive as soon as possible.
"Legislation is clear that if an Executive is not formed by 28 October the secretary of state will come under a legal duty to call further elections to the Northern Ireland Assembly."
Secretary of State Chris Heaton-Harris has said he will be legally obliged to announce a new election date if parties don't come to agreement by Friday 28 October.
Meanwhile, political leaders in Northern Ireland have been reacting to her dramatic statement made outside 10 Downing Street on Thursday afternoon.
Ulster Unionist Party Leader Doug Beattie tweeted: "Unbelievable... yet believable."
In a statement, he added: “Back in July as Boris Johnson was preparing to leave office, I said that the United Kingdom needs strong, stable Government and that this was especially the case with regard to Northern Ireland in the absence of the devolved institutions.
“Three months on, another Prime Minister is about to depart and nothing has changed. If anything the situation is even worse in terms of the cost of living crisis and uncertainty caused by the Northern Ireland Protocol.
“Whoever emerges as Prime Minister, he or she needs to devote some time to restoring devolved Government in Northern Ireland and reverse the damage done to the Belfast Agreement by the NI Protocol. That will not be facilitated by an Assembly election - at the cost of £6.5M - a mere five months after the last one, because such an election will not resolve the issues around the protocol.
“I would therefore urge the present prime minister to act now to ensure that an Assembly election is not called until a new prime minister is in place; a new Secretary of State for Northern Ireland appointed and that the new Secretary of State has time to engage with the political parties in order to work in the best interests of Northern Ireland.”
Liz Truss's position as leader of the Conservative Party after a tumultuous premiership is the shortest in UK history.
She said there would be a leadership election to replace her "to be delivered within the next week" after meeting with King Charles to offer her resignation.
SDLP Leader Colum Eastwood has called for a general election.
He said: "Liz Truss’ Tory government shredded its political authority and economic credibility when they promised unfunded tax cuts for the mega-rich while working people were left to a market meltdown that sent mortgage rates through the roof.
"The Conservative Party has no mandate to govern. Moving the deckchairs around the Tory Titanic will not deliver the radical change that people in Northern Ireland need in terms of support from the cost of living crisis, help to address soaring interest rates and the restoration of devolved government.
"It is far beyond time for a change of government in London and a new Labour led administration that will put an end to this disastrous Conservative rule."
First Minister designate and Sinn Féin Vice President Michelle O'Neill described Liz Truss' resignation as "chaos."
Reacting to the news on Thursday afternoon she said the recent political turmoil in Downing Street has been "disastrous."
Meanwhile, Sinn Féin President Mary Lou McDonald gave her reaction.
In a statement she referred to Ms Truss' tenure as "dysfunctional."
She said: “Forty-five days of chaos and dysfunction at the heart of the Tory Party has ended with the resignation of Liz Truss."Forty-five days that worsened an economic crisis and fuelled political instability in the north, while punishing ordinary workers and families who are struggling to heat their homes and put food on the table.“Forty-five days which laid bare the damage that Brexit has caused Britain politically on the international stage and which has deepened the conversation on constitutional change.“This is a rudderless Tory government which has no mandate in Ireland.“Liz Truss' legacy will be soaring mortgage payments, wrecking the economy, lifting the cap on bankers’ bonuses and working in the interests of the super-rich.“Only a locally elected Executive and Ministers working together will properly serve the interests of people here.“The clock is ticking with eight days left to restore the Assembly and form a government."Just a little over 24 hours before she resigned, Ms Truss had told MPs she was a “fighter, not a quitter”.
Ms Truss said she was elected by the Conservative Party with a mandate to change the situation facing the UK.
"We delivered on energy bills and on cutting national insurance."We set out a vision for a low-tax, high-growth economy that would take advantage of the freedoms of Brexit.
"But she said the situation had prevented her from delivering on that mandate.
With her husband Hugh O’Leary alongside her, Ms Truss said: “I came into office at a time of great economic and international instability.
“Families and businesses were worried about how to pay their bills.
”Vladimir Putin’s “illegal war in Ukraine threatens the security of our whole continent”.
She said the UK had been “held back for too long by low economic growth”.
Her resignation comes after a chaotic day at Westminster that left Ms Truss battling open revolt as the number of Tory MPs demanding she goes continued to rise.
Earlier, Ms Truss met with the chair of the 1922 Committee of backbench Conservatives Sir Graham Brady.
In response, Keir Starmer MP, leader of the Labour Party, said the Tories "no longer has a mandate to govern" and called for an immediate general election.
“After 12 years of Tory failure, the British people deserve so much better than this revolving door of chaos. In the last few years, the Tories have set record-high taxation, trashed our institutions and created a cost-of-living crisis.
"Now, they have crashed the economy so badly that people are facing £500 a month extra on their mortgages. The damage they have done will take years to fix," he said in a statement.
Liberal Democrat leader Sir Ed Davey also called for a general election following the Prime Minister’s resignation.
“We don’t need another Conservative Prime Minister lurching from crisis to crisis,” he tweeted.
“We need a general election now and the Conservatives out of power."
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