Margaret Thatcher threatened to scrap a visit to Ireland because it was being "unfriendly" about the Falklands War, newly declassified files reveal.
The then prime minister was also in no mood to meet with taoiseach Charles Haughey because of Ireland's plans to back calls for a ceasefire in the conflict off Argentina.
State documents show how Britain pressurised Ireland during one of the most critical stages of the war to abstain from a planned United Nations resolution calling for an end to military action.
They believed every vote was crucial and Ireland had let it be known it was in favour of a ceasefire and would likely vote in favour of it.
An unnamed Irish diplomat at the UN attending lunch with then Conservative Foreign Secretary Francis Pym sent a cable back to Dublin warning about the threats coming from London.
The deterioration in relations was particularly disappointing to Mrs Thatcher, who had accepted the "unique relationship" between the two countries, he told the Irish official. He told Dublin in a cable:
In her present mood he could not give any assurance that the PM would wish to have a meeting with the taoiseach, although he added that a week is, of course, a long time in politics and things could change.
According to the files, just released into the National Archives under the 30-year-rule, Mr Pym asked Ireland to at least abstain from a UN vote on a Panama-Spain proposed resolution to the Falklands crisis, calling for an immediate ceasefire.
But the diplomat wrote:
I gave him no hope of this in light of our stand in the (security) Council and explained our policy at some length.
At the lunch, the diplomat also had a conversation with Sir Antony Acland, then head of the British diplomatic service in his role as permanent under-secretary of the Foreign office. The Irish diplomat wrote to Dublin:
Sir Antony referred to the Prime Minister's personal involvement in the Falklands crisis and said that she saw herself in the role of defending the islanders from aggression and of upholding (security council resolution) SCR 502 which calls for immediate Argentinian withdrawal.
I insisted we were in favour of a ceasefire leading to peace in the interests of all concerned, including the islanders and that it was this approach which had guided out actions at the UN.
In the event, Britain vetoed the ceasefire resolution and two days later the Versailles summit supported the British position on the conflict.