Margaret Thatcher claimed the Irish government was living in the era of the Black and Tans in a row over extraditing IRA suspects, state papers have revealed.
Minutes of the meeting the PM had with taoiseach Charles Haughey at the end of 1987 showed she was deeply angry and exasperated at the impasse.
The two leaders met on the fringes of a European summit in Copenhagen where Mrs Thatcher warned the taoiseach she could have done without the Anglo-Irish Agreement.
“I am very angry about all this. My feelings go deeper than anger,” she told Mr Haughey.
“I know now from what you told me that you have extreme difficulties with your people, but where are they living?
“They are going back to the black and tans – or is it 400 years ago? The way they act shows the way an Irish court would behave with our attorney general.”
The report on the meeting at the start of December 1987 was marked personal and secret.
Released under the 30-year rule, it shows the two leaders completely at odds on extradition reform and the need to simplify the transfer of IRA suspects to the UK.
The tone of the meeting was striking as only months earlier Mr Haughey had been urged to handle Mrs Thatcher carefully.
He was briefed that she was prone to lecture and preach about security cooperation.
The taoiseach was told of a dilemma in dealing with the PM’s “personality and approach” while balancing the need to fight the Irish corner by being patient with Mrs Thatcher.
“There will therefore be a continuing need to consider how to handle this propensity of Mrs Thatcher to seize on and pursue some issue where she feels she is in the right, in a single-minded, not to say self-righteous way,” the note said.
In Copenhagen Mrs Thatcher told the taoiseach: “I did not have to sign the Anglo-Irish Agreement. I could have got by without it.
“The only thing it has brought me is criticism and bad blood with the unionists.”
At one point Mr Haughey clearly tried to charm Mrs Thatcher, urging her to show the same fortitude she put into EC budget negotiations.
“Keep trying. You are one of the most able politicians,” he told the PM.
For Mrs Thatcher’s part she appeared unmoved by Mr Haughey’s approach, choosing not to respond to the flattery directly.
Instead, she went on to warn that the dispute over extradition came against the background of the Enniskillen bomb the previous month and the Eksund arms seizure in France, which included two tonnes of Semtex from Libya, in late 1987.
Mr Haughey pleaded with the PM not to go public with the dispute over how his government was overseeing extradition laws.
“Don’t say we did this unilaterally or broke faith. Give the new system an opportunity and we will see that it does work properly,” he said.
Mrs Thatcher closed off the row with a note of resignation: “We will try it: we have no option.”