Thatcher's shock admission that UK got it wrong on Irish border in 1921
Former Prime Minister Margaret Thatcher told officials from the Republic of Ireland that the UK "got it wrong in 1921" with the Northern Ireland border.
A series of extraordinary admissions between Mrs Thatcher and Taoiseach Garret FitzGerald emerge in previously classified papers made public for the first time today.
Documents released in Belfast, Dublin and London provide a new insight into political developments on both sides of the Irish Sea in the late 1980s.
They have been made public under the 30-year rule, which has seen a trove of previously secret Government papers declassified.
Both leaders were in close contact throughout 1986 as the UK and Republic attempted to stand behind the Anglo-Irish Agreement amid growing unionist anger.
The agreement had granted the Republic a formal role in Northern Ireland for the first time.
The Prime Minister and Taoiseach met on December 6, 1986, in London - and Mrs Thatcher made a series of blunt admissions in assessing the security situation along the border.
"You (the Republic) haven't the resources to maintain protection on the other side of the border," she said.
"I do feel very depressed at times about the whole situation. The violence has not been defeated. The SDLP have not done what we are expecting them to do.
"However, it is Christmas - and I had better stop feeling depressed," she said.
Mr FitzGerald praised the RUC for the work it had done in co-operating with the Garda.
"And he pressed for all UDR patrols to be accompanied by the police.
But he warned: "Both forces have a next-to-impossible border to watch."
Mrs Thatcher bluntly admitted: "Yes, we got it wrong in 1921."
The meeting concluded with one Irish civil servant noting: "The Prime Minister then went on... including a rather wistful reference to whether she could continue, in all seriousness, to send young men to their death in Northern Ireland."
Both Governments expressed repeated concerns about the security situation.
This was due to the upsurge in unionist and loyalist protests and demonstrations over the Anglo-Irish deal.
Mrs Thatcher warned that such a reaction was "negative and very dangerous".
"The unionists are saying they have lost everything and have got nothing," she said.
One briefing note warned that RUC Chief Constable Sir John Hermon (below) was "genuinely frightened" by the implications of one demonstration at Hillsborough.
Another briefing note warned that: "Dublin has not grasped the fundamental reality that Northern Ireland is and will remain ungovernable."
Files released by the Public Record Office in Belfast include new insights into Anglo-Irish relations in the 1980s.
One memo from the British Ambassador to Dublin stated "if it were not for history we should get on well with the Irish", noting good relations on every matter - except Northern Ireland.
In London, the files shed new light on the fall of Mrs Thatcher after 11 years in power.