Noel Dorr is the politest of men, but the most difficult of subjects to interview, even if he is so engaged in the conversation over a lunch near Trinity College that he barely touches his food.

Now a vigorous 91-year-old, Dorr has spent a lifetime involved in Irish diplomacy, remaining as interested today as when he retired as the Department of Foreign Affairs’ most senior official 30 years ago last June.

The lunch was sought to talk about the 40th anniversary of the Anglo-Irish Agreement, one in which Dorr was a central figure as the then Irish ambassador to London, but not just that agreement.

Instead, with little effort, the lunch roams over 700 years of history, and the consequences of history.

The rule to the interview, if the word can be used about so polite a man, is that the conversation is less about him, but, rather, more about the things he is interested in. And he is interested in many things.

But, first, the Anglo-Irish Agreement, a treaty signed in Hillsborough by Margaret Thatcher and Garret FitzGerald on November 15th, 1985 that gave Dublin for the first time a voice in Northern Ireland’s internal affairs.

The road to Hillsborough could be said, perhaps, to have begun in London in May 1980 at the first meeting between Charles Haughey and Thatcher – the famous “silver teapot” summit, one witnessed by Dorr.

The Georgian teapot might never have been presented if then minister for foreign affairs Brian Lenihan had listened to Dorr’s advice: “I tried to persuade Lenihan to persuade Haughey not to give her the gift.

Garret FitzGerald and Margaret Thatcher at the signing of the Anglo-Irish Agreement in 1985, flanked by then