Former British Prime Minister Margaret Thatcher suggested removing nationalists from the north during the Troubles.
The startling suggestion is said to have been made during a meeting with close advisors.
The claim is made by former Irish civil servant Michael Lillis in a new book `Brokering the Good Friday Agreement: The Untold Story', which is by Irish civil servants and advisers.
The suggestion has echoes of Oliver Cromwell's infamous "to hell or Connaught" policy of removing the native Irish from their land in the 17th century.
"That crazy episode happened inside her own circle of advisors,"Mr Lillis said.
"She asked at a meeting with her advisors, `Why can’t those people who don't want to be in the UK be moved to the Irish Republic?'
"It wasn't quite a proposal. It was just off the top of her head. Her closest advisors were at the meeting, including Geoffrey Howe [foreign secretary], David Goodall [a diplomat] and Robert Armstrong, who was cabinet secretary.
"She said, `Wasn’t there a precedent for this?' Goodall said, as a sort of a joke, `You remember, of course, prime minister, Cromwell removed a lot of the Catholic people from their lands to the west?'
"The advisors said that was one of the sources of resentment Irish people had, and she backed off the idea," he told the Sunday Times.
Mr Lillis was part of the team involved in the Anglo Irish Agreement, which was brokered between Ms Thatcher and former Taoiseach Garret FitzGerald.
"We learnt that, in her internal consultations (Thatcher) had even urged a consideration of repeating Cromwell's dispersal of the Irish to Connaught (or to hell!) by removing, on that very precedent, the Catholics across the border from Northern Ireland," he wrote.
In the book Daithí Ó Ceallaigh, who worked with the Department of Foreign Affairs, reveals that he and Mr Lillis made wills before moving to the Anglo Irish Intergovernmental Conference at Maryfield, outside Belfast, in the 1980s.
He also claims that their families were kept under 24-hour protection in Dublin while they worked in Belfast.
