'When people say 'I'd like to read a book about the French revolution,' I say well then don't read my book, read Simon Schama." In anyone else this could be seen as false modesty, in Lady Antonia Fraser it is simply -- as she sees it -- being honest. I'm not very good at the big picture, I think I'm actually at my best at biography. I think a lot of people who read Marie Antoinette will then go and read Citizens (by Schama) because it is very good."
Marie Antoinette is itself a radical departure for Antonia Fraser being her first foray into non-British histroy. "on the whole you do brave things if you don't know that they're brave," she says with a smile that still, at nearly 70, has the mistakeable charge of beauty known and accepted.
"What I really missed was knowing things instinctively. I know the rules of the British peerage instinctively. Probably what I did know about French aristocracy before I began was mostly got through Proust. Funnily enough when you have worked as long as I have that was both stimulating and challenging. It was on King Arthur, followed by one on Robin Hood. ("I was only 23, you know.") Then came marriage to Sir Hugh Fraser and five children. Only in her 30s did her career really take shape with her seminal biography Mary Queen of Scots. From then the pattern was set: all her subjects in one way or another have had a bad press.
Was this a conscious decision to avoid the same territory as her mother Elizabeth Longford who by then had already published her biography on Queen Victoria, followed by one on Elizabeth I? Or was it simply a natural desire for justice?
"It certainly wasn't a conscious process because I saw my next subject, Cromwell, as being as far away from Mary Queen of Scots as possible. However, I now realise it is true. I am very interested in the gap between myth and reality and there is a gap, and for me one of the things I really enjoy is checking out the best known stories with a view to demolishing them or finding that they're true."
It was certainly nothing to do with her mother, she says, "although I can understand why you should think so. In fact, my mother didn't in fact write her first book until I was 35 and the mother of five children. In my childhood and my youth she was really a politician like my father."
Antonia Fraser doesn't need to point out that her father is Lord Longford. She is a fixed star in the firmament that conjoins the British aristocracy with the British literati, and as the wife of Harold Pinter for the past 20 years, is at the epicentre of the British intelligentsia, if such a thing could be said to exist.
Lady Antonia (the rules of the English peerage dictate that the daughter of an Earl is thus addressed) knew little more about the French Revolution before she started than anyone else.
"I had read a lot of new feminist history which goes into characters like that and I thought she was ill used, but I hadn't realised what an interesting character she was."
When I suggest that one couldn't help but notice the poignant similarities to the life of Princess Diana - young virgin bride, given no help at court, keen on fashion but decried for being a spendthrift - she bridles.
"Although she is someone I very much admire, I just think as a point of principle it's not permissible to have a character and then give them a lot of thoughts, which she does in Lord Edward Fitzgerald, which I reviewed, so I had to think about it a lot. I'm very traditional, if I speculate, I say so. As someone said at a recent conference I went to, if you want to write that kind of imaginative stuff, what is wrong with writing a novel and calling it a novel?"
However, Antonia Fraser reserves the full force of her opprobrium for the "latest horror", the American historian Edward Morris, official biographer of Ronald Reagan who "decided to put himself, as a character throughout Reagan's life. There he was, the only person who had access to all the papers, and he has Edward Morris at Harvard, Edward Morris in Hollywood, Edward Morris at the White House. I was appalled by this. It was as though was mucking about at Versailles. He doesn't tell you what is invented and what's not. This is actually the end of the line. Barbara Walters as the series started even before Angela Rippon became the face of BBC news.) The experience proved surprisingly useful, she believes, in writing her two latest books, The Gunpowder Plot and Marie Antoinette, where she wanted the reader to be gripped by the narrative as if not knowing the ending.
"Writing whodunits you get used to dealing out clues, but not too much, so when people look back they can say, 'yes she didn't cheat.' Because you force yourself all the time to think, what did she know at this time, what could she legitimately have expected? I think I am the only person to have pointed out that Marie Antoinette actually expected to get off. Why shouldn't she? She hasn't heard the end of the story. And there was no tradition of killing consorts. Consorts were not executed, they were repatriated or ransomed. And I don't think I would have got that, really, if I hadn't all the time forced myself to stay in her world."
The book she is most proud of is a study of the lot of 17th-century women - written after her account of Cromwell - The Weaker Vessel. However, it was not a success, at least this side of the Atlantic. In the States it was a different story, marketed as feminist history rather than biography, which, she says it wasn't. Marie Antoinette is a prodigious work of scholarship. It took five years to research and write.
Had she never thought of becoming an academic where commercial publishing constraints are less relevant?
"I was brought up in Oxford, my father was an academic all my childhood, I went to university in Oxford. I very much thought of NOT becoming an academic and I did not want to marry a don - I can't remember if a don ever asked me. No I wanted to go out and have life."
The brainy and beautiful Lady Antonia Pakenham had no shortage of suitors and married Sir Hugh Fraser when she was 24. Because of her name, and because of Mary Queen of Scots, people imagine, she says that she is herself Scottish, although in fact Longford is an Irish earldom.
"I am literally the daughter of the ascendancy. The Earls of Longford were Protestant earls. My father converted, and then my mother. I became a convert when I was 14 which is a strange trajectory, but I feel rather good about it, because it was a positive decision."
I had passed Harold Pinter at the door of their Holland Park house, off to a preview of The Homecoming, which was about to go to Dublin, then to the US. Lady Antonia takes ever opportunity to go back to Ireland. "Over the last seven or eight years there have been two Pinter Festivals in Dublin and Harold was in the last John Boorman film that they shot in Ireland and we went and stayed in a luxurious hotel by Dalkey, which I loved.
"Dublin now is so different from the Dublin of my youth and I've been going to Ireland all my life. We went on through the war because my brother was heir to my uncle and we used to just go off and stay with my great uncle, Lord Dunsany, at Dunsany Castle.
"I still feel at home in Ireland in a strange way, perhaps not so strange if your ancestors have lived there for 400 years and your brother (Thomas Pakenham) lives there. The children used to say, what are we? We used to say you're half-Irish and half-Scottish and half-English. They got quite old before these mathematical geniuses could see what was wrong in that. But I think because of my work, I am half-Irish, half-English and half-Scottish."
Marie Antoinette by Antonia Fraser is published by Weidenfield & Nicholson, £25 in UK.