Margaret Thatcher threatened to scrap a visit to Ireland because it planned to support a call for a ceasefire in the Falklands war in 1982.

Previously unpublished state documents revealed yesterday how Britain piled pressure on Ireland during one of the most critical stages of the war to abstain from a planned United Nations resolution calling for an end to military action over the contested ownership of the islands off the coast of Argentina.

An Irish diplomat at the UN attending lunch with then Conservative foreign secretary Francis Pym sent a cable back to Dublin warning about threats coming from London.

During the lunch Mr Pym said he deplored what had happened to Anglo-Irish relations which he described as "getting worse every day.

"In her present mood he could not give any assurance that the PM would wish to have a meeting with the taoiseach, although he added that a week is, of course, a long time in politics and things could change," he said.

According to the files, just released into the National Archives under the 30-year-rule, Mr Pym asked Ireland to at least abstain from a UN vote on a Panama-Spain proposed resolution to the Falklands crisis, that called for an immediate ceasefire.

But the diplomat wrote: "I gave him no hope of this in light of our stand in the (security) council and explained our policy at some length."

In the event, Britain vetoed the ceasefire resolution and two days later the Versailles summit supported the British position on the conflict.