Newly released state archives reveal the 1982 war over the South Atlantic islands triggered the greatest crisis in Anglo-Irish relations since the Northern Ireland conflict erupted in 1969.
Such was the fury in the UK over the perception that Ireland had sided with Argentina that the Irish embassy in London warned Dublin they had never received such a flood of anti-Irish sentiment since Lord Louis Mountbatten was blown up by the IRA in Sligo.
The Irish embassy supplied detailed daily dossiers to Taoiseach Charles Haughey on rising anti-Irish sentiment in the UK – including a claim by Conservative backbenchers that Ireland had "stabbed her oldest ally in the back".
The embassy had also raised concerns about a retaliatory campaign by Tory MPs to have Irish citizens barred from voting in and contesting UK elections.
Ian Gow MP, who was killed by the IRA in 1990, had deplored Ireland's stance and, in a briefing note to Dublin by Ambassador Eamon Kennedy, was described as having "compared her (Mrs Thatcher) not only to Churchill and de Gaulle but to Good Queen Bess herself".
In a blunt message on October 28 to the Taoiseach by the British embassy on the personal instructions of Mrs Thatcher, Ireland was effectively warned not to back Argentina's claim to the Falklands or Malvinas.
That was ahead of a key UN vote where Argentina, whose forces had been defeated by a British task force, was seeking negotiations over the Falklands' sovereignty.
"I very much hope I can look forward to Ireland not to side with Argentina against Britain in the coming debate," Mrs Thatcher wrote.
"There is much support for our position in many parts of the world. I am writing to ask you for your understanding and support. Argentina envisages only one possible outcome to any such negotiations, the transfer of the islands to herself against the wishes of the people who live there."
The previous May, the British ambassador told the Taoiseach he was "dismayed" to read a statement by the Irish government effectively suggesting an end to an EU ban on Argentinian exports.
That followed a personal message to Mr Haughey on April 6 from Mrs Thatcher in which she sought Ireland's "urgent help" in bringing pressure to bear on Argentina to withdraw from the islands.
Meanwhile, the British ambassador to Dublin in 1982, Leonard Figg, said that while few Irish people knew where the islands were prior to the conflict, they identified with Argentinians as a "fellow victim" of colonialism.