Taoiseach Micheál Martin has said that Britain must appoint a new prime minister as "quickly as possible" to ensure political and financial stability after Liz Truss's resignation.
Arriving at a European Union summit, Mr Martin said that stability is "very important and we would like to see the UK system within its capacity to have a successor selected as quickly as possible and that stability would be brought to the situation, given the fairly significant geopolitical issues facing Europe".
"On a personal, level I sympathise with her. I think it's been a very difficult time for the British prime minister, given all that has happened."
He said there was a window of opportunity for Truss' successor to address the issues around the controversial Northern Ireland Protocol Bill, which would unilaterally change the protocol.
"I don’t see it getting past any time soon in the House of Lords, at least that’s what we’re being told," he said.
He concluded: "We are obviously concerned when there is instability [in the UK] but I believe it is within the capacity of the British system to settle this down. We look forward to an engagement with the new prime minister."
In a statement this afternoon, Mr Martin said he had a number of opportunities to engage with Ms Truss during her "brief period" as prime minister.
"I convey my best wishes to her and her family, following today's announcement of her resignation," Mr Martin said.
"Working together to protect the gains of the Good Friday Agreement and to support peace and stability in Northern Ireland continue to be vital responsibilities for the British and Irish Governments, particularly now in the absence of a functioning Northern Ireland Executive and Assembly," he added.
Mr Martin said that "substantive EU-UK engagement" to reach agreement on outstanding issues around implementation of the Northern Ireland Protocol is "ever more urgent".
"Britain is Ireland's closest neighbour and a relationship of partnership between the British and Irish Governments is vital for peace and prosperity on these islands."
Issues facing the British political system have 'flowed' from Brexit, Taoiseach Micheál Martin has said following the resignation of Prime Minister Liz Truss.
— RTÉ News (@rtenews) October 20, 2022
He said many issues had 'not been thought through' at the time of the vote in 2016 | Read more: https://t.co/edqpYoyE1b pic.twitter.com/gHZsGNoqfw
Speaking to RTÉ News' Six One, Minister for Foreign Affairs Simon Coveney said that while the "mood music had improved" in recent weeks, Ms Truss's resignation means that "we're back to instability again".
"I've had the privilege of being a Foreign Minister for five years and in that time, I've dealt with six Secretaries of State for Northern Ireland, five Foreign Secretaries and now it's going to be four Prime Ministers," he said.
"We're trying to get complex issues negotiated and we're trying to find compromises in a very heated and difficult political environment, particularly in the context of Northern Ireland.
"From an Irish perspective, this isn't really about personalities. It's about stability, and about having a partner to negotiate with that can help us solve problems together and that's what we want to focus on."
Mr Coveney added that part of the consequence of what is happened today is of course more uncertainty for Northern Ireland.
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"Because not only will we have a new British Prime Minister next Friday, but of course, if there isn't an Assembly up and running in Northern Ireland by next Friday, well, then by law, whoever is Secretary of State at that time, is required to set a date for a new election."
Minister for Finance Paschal Donohoe said Ireland is monitoring the effect that political developments in the UK could have on the Irish economy.
Mr Donohoe said the political and economic stability of the UK is a "vital ingredient in the economic prospects of Ireland and indeed of Europe".
Speaking in Dublin, he said that the UK government has "reaffirmed their commitment to budgetary and economic stability".
"Ireland has always been a close friend of the UK and of the government of the UK. Even during tough and challenging moments during the Brexit process, we always affirmed the value of close friendship," he said.
"We really looked forward in the time ahead to continuing that close friendship and cooperation with the new PM."
Former Taoiseach Bertie Ahern criticised Ms Truss, describing her stance on the Northern Ireland Protocol negotiations as unhelpful.
Mr Ahern said he hopes whoever becomes the next prime minister will take a "proactive" approach to the talks with the EU.
The former Fianna Fáil leader, one of the architects of the Good Friday Agreement, told an Oireachtas committee that the prime minister had changed on his way through the door of the committee.
"Quite frankly, I didn't think it was helpful what the British prime minister of yesterday said, so maybe whoever is there tomorrow might say something different," Mr Ahern said.
"What she said yesterday was that even if there was negotiations, that what was in the legislation would be the bottom line.
"Now, I never tried negotiations that declared the bottom line before I went into the negotiation, so that's clearly not going to solve anything."
Ms Truss said on Wednesday that she was "completely committed" to the Northern Ireland Protocol Bill and that negotiations with the EU will reflect "the same position".
Sinn Féin vice president Michelle O'Neill called on political parties in Northern Ireland to unite to "stand up to the Tories", following the resignation.
The chaos & disastrous policies of the Tories has heaped misery onto workers & families
— Michelle O'Neill (@moneillsf) October 20, 2022
Liz Truss joins the long line of British Prime Ministers who have failed people
We need all parties in the North to work together, stand up to the Tories & support people in a new Executive
"The chaos and disastrous policies of the Tories has heaped misery onto workers and families," she wrote on social media.
"Liz Truss joins the long line of British Prime Ministers who have failed people."
The British Irish Chamber of Commerce called on Ms Truss's successor to find practical solutions to the Northern Ireland Protocol and work to restore the EU-UK relationship.
John McGrane, Director-General of the British Irish Chamber of Commerce, said he acknowledged the efforts of Ms Truss to begin restoring the British-Irish relationship and addressing the issues related to the Northern Ireland Protocol.
Additional reporting: Paul Cunningham, PA
