He lives in a magnificent old period residence on Killiney Hill Road, overlooking Killiney Bay and overlooked by the obelisk on Killiney Hill. He shares the house with his wife, formerly Ms Elizabeth Young (daughter of a Glasgow doctor), and five children aged between 16 and 30.

He doesn't look like a Fianna Fail type - he is very much the landed gentry type. It's the tall defiant stature, the shock of lush hair, the accent and the laugh. It's a choking convulsive laugh, invariably triggered by reflections on himself. And, oh, the niceness. An Anglo-Irish niceness. There is no edge to him. He is faultlessly polite, even self-effacing at times. He is also clever, very clever in a light-handed way.

He was born in Surrey, England, on the last day of 1946. He lived almost all of his early life in England (with regular trips to the old family home in Co Tipperary during summers); school at Canterbury Cathedral Close (lots of atmosphere); and later to Christ Church, Oxford, where he did philosophy, economics and politics, majoring in philosophy. He did a PhD in French history.

His father was the renowned historian, Mr Nicholas Mansergh. Among the latter's books were The Irish Question and The Commonwealth Experience. The father, according to Martin, was very much caught up in the excitement of creating a new State. He had his first book, The Irish Free State, published in 1934.

He died in 1991, and a selection of his essays, Nationalism and Independence, was published posthumously. It was edited by Martin's mother, Ms Diana Mansergh, who died earlier this year.

Martin completed his PhD at the Mansergh family home in Co Tipperary and then applied for a position in the Department of Foreign Affairs, which he joined in the autumn of 1974. He was involved in Ireland's first presidency of the European Economic Community (as it then was) in 1974 and was then posted to the Embassy in Bonn, where the late Mr Robin Fogarty was ambassador.

Martin moved back to Dublin in 1977 and was at Iveagh House until 1980 when he was asked to move to the Taoiseach's office to write scripts for Mr Charles Haughey and to work on joint studies on North-South issues arising from the Haughey-Thatcher meeting of 1980.

Then when Mr Haughey lost power in July 1981, Dr Mansergh offered and was asked to come with him into opposition, which necessitated his leaving the Civil Service.

He moved from paid, secure, pensionable employment with hesitation to a position where you could be gone at 24 hours' notice. A colleague in the Taoiseach's Department said he would last no more than six weeks.

"I'm still there 20 years on", a reflection which occasions a laugh.

VB: Why did you agree to leave the Civil Service for a precarious role with Charlie Haughey?

MM: Well, I suppose there were two reasons. I was interested in working with him, I admired him. A secondary, a private reason would be, partly because of co-ownership of the farm in Tipperary, I didn't want to spend my whole career abroad (with the diplomatic service). I enjoyed my time in Foreign Affairs. I learned a lot and I suppose I would be one of those political advisers whose had good civil service training and who, at least once at one time, passed his exam to get into the public service even (the laugh again) if that is not the basis on which I hold my present post today.

VB: You said you admired Haughey. What did you admire about him?

MM: Well, I mean he was somebody who had a very strong political track record over the previous 20 years. He had been a very capable minister. Haughey was a tough guy and, you know, challenging to work with, but I enjoy challenges.

VB: He has often been accused of demeaning people he worked with. Was he like that to you?

MM: I felt, I must say, the vast majority of the time he treated me with respect. We had a very close working relationship. I mean I'm not talking about the first six months period when I was a civil servant, I mean subsequent to that we had a very close working relationship and you know, quite frankly, if he had been contemptuous of me, I wouldn't have bothered, I'd have walked away.

VB: He was back in office, of course, in March of the following year (1982).

MM: I was rather pleased with that because that's what you would call knock-out opposition. I mean Garret FitzGerald had come in on the 30th of June 1981, for all anyone had known, he could have been there for four years anyway, despite the tight situation. He (Haughey) was actually out of office for only seven months. I think it was a very effective period in Opposition. As a matter of fact, I was less surprised than Haughey the night the Government fell.

VB: Why is that?

MM: I think he just didn't believe it could happen. Now to be fair to Martin O'Donoghue, he made quite a most effective response to a budget that I have ever heard, very short, didn't last more than quarter of an hour, a clinical demolition of it and I'm sure that had a lot of influence on the fall of the Government [this was the John Bruton budget of January 1982].

VB: Were you involved in the deal Charlie Haughey did with Tony Gregory which secured his return to government in March 1982?

MM: Yes. I was involved in researching it and sort of putting together the different bits. Haughey would have told me who to talk to about this and about that, and before he went to see Gregory the first time, you know, I would have given him a paper on Gregory's position on different issues. I think he was quite well prepared going into meetings both with Gregory and with the Workers Party.

VB: And then there was the GUBU Government period from March 1982 to November 1982.

MM: I was the Northern Ireland political adviser during that period, so I suppose I was mainly involved on that side of things. That was the period of the (Jim) Prior initiative and also the Falklands. Anglo-Irish relations were very difficult. It was really the last time the British did a solo run political initiative, the result of which would have been an internal settlement which the SDLP and others thought would have resulted in a return to majority rule. During that time also, a coherent economic plan was formulated which, if allowed to be implemented, could have avoided much of the economic damage that later was caused. I had occasion to view the Haughey-FitzGerald debate for the November 1982 election some years later, and in that, FitzGerald, the social democrat, argued there was scope for more taxation and Haughey argued that there had to be spending cuts. I believe Haughey was right.

VB: You were in danger of losing all after the November 1982 election, for not only did Haughey lose power but he was nearly dislodged as leader after the revelations of the telephone tappings.

MM: I would be more conscious in hindsight, perhaps, how close to the precipice I was stepping than I would have been at the time. It was a very intense period but, mind you, I suppose lots of people had a belief in Haughey's capacity to fight and survive. It was a very close run thing, I mean I think he was at one moment very close to resignation. Now he would have talked to lots of people other than me, but I suggested he should play for time.

VB: Did he tell you he was resigning?

MM: He got so far as drafting a few lines of a statement on which I did some further work, but my heart wasn't in it. I certainly remember him saying to me when I said he should try and gain some time, he said I mentioned those historical analogies of de Gaulle in 1968, and Frederick the Great who had his back to the wall in the seven years war before the Tsarina Elizabeth died. He said well if he thought that (he could play for time), he'd fight.

He did a lot of soundings so I'm not suggesting that anything I said to him had any particular influence. But I mean I would have been one voice among others, that's all. I would have helped him throughout the period. I would be sort of proud of having helped him fight his political battles.

VB: One of the issues that arose when Fianna Fail were in Opposition from 1982 to 1987 was the Anglo-Irish Agreement of 1985. Haughey was doggedly opposed to it, he said it was unconstitutional. He indicated he would reverse it when he returned to power and he sent Brian Lenihan to America to lobby against it. Were you happy with all of that?

MM: I think it would be fair to say, and this is with the benefit of hindsight, that we misread the constitutionality (of the agreement). I think too it is fair to say that we also underestimated the attractions of, you know, the much closer working relationship with the British Government on Northern Ireland. It had been expected that there would be a number of specific reforms as part of that package but that did not materialise. But I mean Haughey took the view that once the parliamentary battle had been fought and lost, then he would have to work the agreement in Government. I remember him saying in December '85, you know, one often ends up working something in Government that one has opposed in Opposition.

As for the Brian Lenihan trip to America, I think he perhaps found, if you like, that the ground had been well prepared before him (by the Department of Foreign Affairs) and that there wasn't a very receptive audience. With what zeal he carried out the mission, one can only speculate. (Laughs).

Haughey's style in Opposition was robust. People nowadays are critical that the Opposition is not robust enough. People were certainly interested in politics at that time and people were sort of passionately pro or anti-Haughey.

VB: On return to Government, Fianna Fail more of less did what it had criticized the Fine Gael-Labour Coalition government for doing.

MM: No. I don't agree with that. Instead of just engaging in fiscal rectitude and high taxation, we had several economic development initiatives. In the financial services centre, for instance, a tourism initiative, the beef industry initiative which admittedly failed, but there were a number of developments. His idea was to balance necessary cuts to expenditure with economic developments initiatives and social partnership.

In many ways, economically, the country has not looked back since things were taken decisively in hand at that period after 1987. I mean, I regard '87 as being as at least as important a turning point as the Whitaker White Paper in 1958.

VB: During that time also, the peace process was initiated and you were in the thick of that. How did it come about?

MM: A small party delegation of which I was one, Dermot Ahern was another and a party treasurer, Richie Healy from Meath, met Sinn Fein twice in Dundalk, in parallel to the SDLP/Sinn Fein talks in 1988. Haughey had come into contact with Father [Alex] Reid as far back as '86. That was the beginning of my involvement in the peace process.

VB: Did you like Haughey?

MM: Yes and I still do.

VB: Do you see him now?

MM: Yes, I saw him quite recently.

VB: Were you shocked by the revelations of the McCracken Tribunal and the Moriarty Tribunal concerning him?

MM: Well, I mean, he attempted to keep his private life separate from his public life, so obviously I had no idea of the way things were being financed. There has actually been an interim tribunal verdict, the one given by McCracken, and I agree with what he said about the dangers of political leaders financing their lifestyles through private donations.

I would say, as a fact to be taken into consideration, that one of Haughey's first decisions when he became Taoiseach was to cancel the project to construct an official residence for the Taoiseach which would have cost at that time seven or eight million pounds and probably a million or two a year to run. Instead he had a place of his own, if you like, which was suitable enough as a Taoiseach's residence and he didn't bother the taxpayer with it. I think the point should be made that there had been a proposal that the Taoiseach's lifestyle, any Taoiseach's lifestyle, should be supported to a very substantial extent by the taxpayer and he had turned that down.

VB: You were re-appointed adviser on Northern Ireland by Albert Reynolds when he became Taoiseach in February 1992. How did that come about?

MM: I had had friendly relations with Albert for many years before then. He used to come into my office when Charlie Haughey was Taoiseach and we had long chats. Then, after he had been elected leader of Fianna Fail and Taoiseach-elect, he came into my office, I think when he was going down to see Haughey, a few days before he took over, he came into my office and asked me.

VB: At that meeting, Haughey told him about the peace initiatives underway.

MM: I wasn't at that meeting, that's what Reynolds said subsequent to that. Remember relations between the two of them were pretty frosty at the time.

VB: Reynolds never acknowledged Haughey's involvement in that subsequently?

MM: Well, I think he certainly put on the record that discussion.

VB: Albert Reynolds continued the peace process of course. What happened?

MM: What was happening was that in 1988, direct dialogue had been broken off. Father Reid stayed in contact mainly with myself throughout the subsequent period. Various things were tried but didn't lead anywhere until John Hume had a meeting with the Taoiseach, this was Haughey, in the autumn of '91. Drafts were going backwards and forwards and not very fast either. When Reynolds became Taoiseach he took up this with enthusiasm. I believe it was the early autumn of '92, Albert and I agreed that direct contact should be resumed. This time I mean, I was on my own and between '92 and August '94, I met with various Sinn Fein people, mainly Martin McGuinness, occasionally Gerry Adams, Aidan McAteer. I remember Tom Hartley once. The meetings took place usually in the Redemptorist monastery in Dundalk and occasionally in the Redemptorist house in Orwell Road, Dublin.

VB: When did you think that there was something on here, that this is going to lead to a breakthrough?

MM: Well, I mean, one was never certain or confident that it would lead to a breakthrough but the question was/is was the initiative despite all the political risks involved, was/is worth undertaking, did it have at any rate some prospect of success? I suppose it wasn't until towards the end of July '94 that I knew this was going to happen.

VB: Albert obviously was crucial to the process, he had the nerve to keep it going.

MM: Albert was forceful, a risk taker. I remember being impressed, it was about another issue, saying within a week of taking office as Taoiseach that he didn't care if he was the shortest-lived Taoiseach ever. He'd rather do things right and do them his way. And it ended up with him not being there very long. Certainly, if it had come out prematurely that there was dialogue going on, I mean Garret FitzGerald had established the principle that was generally accepted, going back to the 70s, you don't talk to terrorists full stop. I had to undertake what no civil servant could have undertaken at that time and I was fully conscious of the fact that if it came out in the wrong way at the wrong time, I would be out on my ear within 24 hours.

The argument against contact would be that you might convey the impression to people that they were winning and that, if anything, they might sort of pile on physical pressure. This was one of the reasons the '88 talks were broken off both by the SDLP and ourselves. I mean to make it very clear that we weren't going to take part in open-ended dialogue without a specific end in sight. One would have to be very conscious, I mean there was probably more responsibility on my shoulders at that time, regardless of anything else I ever do in my life or that there will be in the future. I mean, a moral responsibility, a democratic responsibility and above all the responsibility to be straight with people. I mean what would have been quite disastrous would be to tell people what they might want to hear in the hope of persuading them to do something that you wanted them to do. I mean credibility and absolute straightforwardness is absolutely vital.

VB: You say you very much liked Charlie Haughey and admired him, what was your attitude to Albert Reynolds?

MM: I admired his contribution as Taoiseach. He made a huge contribution to getting the peace process over the threshold of the first ceasefire and, indeed, effectively I mean 90 per cent of the framework document was completed when he left office. I admired his "can do" approach and his risk-taking even though he was only there for three years.

VB: When his Government fell and John Bruton became Taoiseach, did John Bruton ask you to stay on?

MM: He did. I think he wanted me to stay on, primarily because of my contacts with Sinn Fein but I felt, and of course one of the conditions was that I would cut off contact with my friends in Fianna Fail, I didn't think that that was a sort of viable proposition apart from anything else. Somebody who sort of crosses the floor politically just to keep a job would arouse suspicion and their credibility wouldn't be the same.

VB: How have you got on with Bertie Ahern?

MM: I mean, he's tremendously hardworking and one has a very easy working relationship with Bertie. He'd be the first Taoiseach that I've worked for that was of the same generation as myself or even a little bit younger.

I cannot recall a single instance, with perhaps the exception of the famous outburst over Gay Mitchell, of Bertie losing his temper. I mean if he's cross, he goes very, very quiet. I am just amazed at the amount of hours he puts in.

He's done very, very well in holding together for more than four years now, I mean a minority Coalition Government. It has never been done before and I think the other thing is that he has a gift, which I think is very rare, very rare in politics, that he is somebody who, if he has a difference of position or he disagrees with somebody, manages to avoid adding any sort of additional antagonism to the situation. He is somebody who has been able to work, have a good working relationship, in fact an astonishing working relationship with David Trimble, Gerry Adams, he has an extremely good relationship with Tony Blair, an ability to get on with people more or less regardless of where they're coming from. That's a rare gift even among politicians. Two areas where the strength of it has been seen is obviously in the achievement of the Good Friday Agreement, in keeping the peace process on the road. But also the defusing of confrontation between the social partners.

In a sense, his career was built on his ability to defuse dangerous industrial confrontations. Arguably the seminal period was the '87 to '91 period as Minister for Labour. His mentor, in a sort of a way, wasn't so much Charlie Haughey as Billy Attley. He is a Taoiseach, and probably the first Taoiseach, who is proud to have cut his teeth as a trade unionist, and a Fianna Fail one at that.