Then prime minister Margaret Thatcher asked her Northern Secretary Jim Prior in 1983 if he believed Britain should organise a “tactical withdrawal” from Northern Ireland.

However, Mr Prior said that would be “utterly wrong” and would mean “civil war”.

Newly-released secret 1983 files, from Mrs Thatcher’s office, also disclose that she doubted whether Britain could solve the Northern Ireland question and concluded that “this must be for the people of Northern Ireland to solve”.

Outlining his two particular worries, Mr Prior said the first was that Northern Ireland was a constant drain on the UK economy and second was the growth in support for Provisional Sinn Féin. He did accept that all those who had voted for Provisional Sinn Féin candidates were necessarily in favour of violence.

The files show that Mr Prior was of the view that “we could not ignore that about 40% of the vote in Northern Ireland in recent elections had been captured by Sinn Féin and the SDLP. And the proportion was growing”.

An account of a meeting between Mrs Thatcher and her Northern Secretary recorded: “The Prime Minister asked whether it was Mr Prior’s basic concern that because the supporters of violence were going to win, we should organise a tactical withdrawal. Mr Prior said that this was not his view.

“He was not suggesting for one moment that we should withdraw troops from Northern Ireland. This would be utterly wrong. He was absolutely convinced that withdrawal would mean civil war. His main point was that he believed it would be a massive mistake to do nothing during the next five years.”

The account, just released under the 30-year rule, continued: “The Prime Minister expressed doubts as to whether we could solve the Northern Ireland problem. This must be for the people of Northern Ireland to solve though we could perhaps act as a catalyst. Agreeing, Mr Prior said that we could also provide a framework within which the people of Northern Ireland could try to solve their problems.”

“But the key was to achieve relations with Dublin which were sufficiently good for Dublin to be persuaded to put pressure on the SDLP [to join the Northern Ireland Assembly which had been opened in 1982].”

It was suggested that if the SDLP could be persuaded to join the Northern Ireland Assembly then it would be possible to devolve five departments – one each to the SDLP, the Alliance and the DUP and two to the Official Unionists.

“The Official Unionists would probably find it hard to refuse this carrot. On the other hand, we should be able to say that this was not power-sharing because we retained responsibility for law and order and finance.”