The Irish Government was left deeply embarrassed after details of a proposed visit by the British ambassador to the Republic were leaked to the IRA.

Mystery surrounded how the terror group got wind of a visit to Sneem in Co Kerry by Sir Nicholas Fenn.

Previously classified files, released in Dublin under the 30-year rule, detail the concern among Garda chiefs, the Irish Department of Justice and Taoiseach Charles Haughey.

The leak was extremely damaging, coming just months after the IRA killed Northern Ireland judge Sir Maurice Gibson and his wife Cecily with a remote controlled bomb near the border.

Unionist officials insisted after the Lord Gibson killing that there was a mole within the Garda. In August 1987 the IRA deliberately leaked to newspapers that it had detailed information about the ambassador's proposed visit to Sneem, a village situated on the Iveragh Peninsula in Co Kerry.

Hours later Sir Nicholas contacted the Irish Government to say he was "besieged" with requests for interviews about the situation.

Sir Nicholas offered to do a single interview with the BBC - and to stress his complete confidence in the Garda authorities and his protection detail.

"It was quite understandable that the ambassador would be under pressure at public occasions here today to say something and it would be useful for him to be able to refer back to an interview he had given," a confidential Department of Foreign Affairs memo said.

"It also seemed to me that a helpful statement by the ambassador expressing confidence in the Garda would be useful in Northern Ireland and in Britain, where I noticed at least one MP calling on the Foreign Secretary to make a protest to the Government here."

The transcript of Sr Nicholas' interview was later supplied to the Irish Government - and he reiterated his faith in the Garda.

He said: "The Garda look after me very well.

"It is true that we learned in advance that the details of my movements had fallen into the hand of subversives, as they call them, and the security was, for that reason, enhanced."

The ambassador said he thought it was "unlikely" that there was a mole at high levels within the Garda - and said it could potentially have been "an unintentional leak", possibly due to a mistake or sloppiness.

Belfast Telegraph