HE PREFACED his recent book on The Decline and Fall of the British Aristocracy by saying that his wife, Linda Colley, had 'contributed more to the making of this book than any other individual' and went on: 'The final version was begun amidst circumstances of scarcely believable joy, but was completed at a time of the most terrible grief. Without her life and her love, I should never have known the one, and could not possibly have borne the other.'

She prefaces her new book, Britons, Forging the Nation, 1707-1837, by acknowledging 'my husband and comrade-in-arms, David Cannadine. Without him, it is not too much to say that I would scarcely have survived to complete this book.'

One does not have to read between the lines to perceive that the marriage of these two eminent historians has been subjected to intense strain - and survived.

It was a marriage made not in heaven, but by the then Master of Christ's College, Cambridge, Sir John Plumb. Linda Colley was a former pupil of his; a young historian who had already acquired a reputation for a brilliant mind and a large ego. In 1979, when she was just 30, Plumb invited her to become the college's first woman Fellow. David Cannadine, himself already a History Fellow at Christ's, felt he should have been consulted, and campaigned hard against her appointment. 'You never know,' said 'Jack' Plumb mischievously, 'you may end up marrying her.' As if to make doubly certain, the Master allotted them rooms on the same staircase.

'Jack was matchmaking and mischief-making, acting like a benevolent despot, which was his style,' Colley recalls. 'But it was no instant romance. David had a reputation as a complete workaholic, so I was surprised to find he had a great sense of humour and absolutely no pomposity.' To soften him up, since he was Director of Studies at Christ's and somebody she was going to have to get along with, she decided to invite Cannadine to dinner, 'to find out what this icy work-machine was really like.' She laid on a specially delicious meal, only to find that the avocado pears essential to the first course were rock hard and inedible. 'I discovered then that he could laugh.'

The two also discovered that they had an astonishing amount in common. 'If they'd run us through a computer in one of those dating agencies,' Colley says, 'they couldn't have found a more perfect match. We both come from lower-middle-class backgrounds: we're classic children of the welfare state - of a kind, incidentally, that could not exist today. Both our fathers were civil servants. We both have a very strong regional background - David was brought up in Birmingham, I'm from the North, so neither of us had standard southern voices. And we're both modern British historians.'

Born within a year of each other, both had obtained brilliant firsts at university and by the late Seventies were beginning to be recognised as outstanding and prolific historians.

'It was three or four months before we fell in love,' Colley goes on, 'and when it did happen we tried to be spectacularly discreet. I was the first woman Fellow in this friendly but very conservative environment and we were both teaching many of the same people, so any overt romance would have been inappropriate.' Cannadine adds: 'Cambridge colleges are notoriously introverted and gossipy communities, and we didn't want to give cause for rumour. We succeeded so well that when I got engaged in 1982, just before Linda left to go to Yale, one of my colleagues asked: 'Who is she?' '

They married that July and spent the first six years of their marriage commuting across the Atlantic. 'There were no prospects for advancement in Cambridge and I was very ambitious,' Colley explains, 'so I accepted the job at Yale. We were in this bizarre situation - newly married and living on opposite sides of the Atlantic.' Cannadine remembers: 'It had its own exhilarations. It was quite fun to catch a plane every few weeks and whizz off to America. It was sometimes exhausting, very expensive, we often felt a bit like characters in a David Lodge novel, and transatlantic phone calls are not the ideal means of intimate communication . . . but it had its compensations.'

Since 1988 Cannadine has been a Professor of History at Columbia University, so they do now live on the same side of the Atlantic, albeit in separate cities - Colley in New Haven, Connecticut; Cannadine in New York. They organise their schedules so as to be able to meet up for long, Thursday-to-Monday weekends. They also share a cottage in deepest Norfolk to which they retreat for three months each summer, and it is here, in England, that most of their writing is done.

When Cannadine was offered a professorship in America they felt they could at last start a family, and soon afterwards their daughter was born. The dedication to Cannadine's Aristocracy gives the stark facts: 'In memory of Harriet Fenella Saffron Cannadine, born 3 February 1988, died 19 March 1988.'

Can they talk about this? Yes. In common with many bereaved people, they like talking about the child they lost: it reaffirms her life, even while it recalls the passionate grief that followed her death.

'I had a very easy pregnancy,' says Colley, 'and completed the penultimate draft of my book on Lewis Namier on the very day that Harry arrived, in that last-minute surge of energy that all the baby books say you will devote to tidying up the house.

'I finished the book at 4 pm and labour started two hours later. She was born the following morning, perfect. The hospital paediatrician complimented me on this healthy baby. Some cot deaths are found to be attributable to some unsuspected defect, but when she died six weeks later, hers was the body of a perfectly healthy baby. What went wrong they never knew.

'With a cot death,' Colley goes on, 'you have no time to contemplate or prepare yourself. It's not like an illness, where someone is not very well, then getting worse, then at risk of dying. With this, 20 minutes ago your child was alive and now she's dead. You're left with the feeling that there must have been a mistake. Harry must be all right. In a couple of hours somebody will bring her round.'

Cannadine felt exactly the same. 'I kept thinking, this is all a dream, I'm going to wake up and everything will be all right. And of course it isn't. It changes your life for ever.'

He recalls that time: 'We emigrated, sold a house, and had the birth and death of Harry all within six months. We grieved in different ways. You felt as though all your skin had been torn off and the nerve endings exposed, and all social interaction became unbearable. It has left me with a permanent sense of the random risk of catastrophe in life. I don't think I shall ever forget that. You lose all sense of the natural order of things - for instance, that it's natural for children to outlive their parents - even though you've only got to read Dickens to know that that's not necessarily true. It's not fear, but a recognition of the transient nature of the human condition.'

Colley takes up his thread: 'It made us different people. Once you know how completely and suddenly the earth can open up at your feet and the worst can happen it also, paradoxically, leaves you more afraid of everything else. David began to suffer very badly from vertigo, which he never had before. I would worry terribly if ever he was late. I'd think, the car has crashed, he's dead, he's been mugged. Yet at the same time you're not afraid of anything because you think, the worst has already happened.

'Later that same year, when we were in England, we heard that our house in America had been hit by a tornado. I just didn't care. After Harry's death, a thing like that didn't matter.'

Cannadine says: 'To this day, the most ecstatically, tinglingly exciting moment of my life was when Harriet arrived, and six weeks later the most scaringly terrible moment of my life was when Harriet died. It's an astonishing roller-coaster of the emotions which nobody who hasn't experienced it can ever imagine and nobody who has can ever forget.'

Colley does not entirely concur. 'A lot is blotted out. Just as one can't remember the pain of childbirth, so you forget the immediate pain of grief after a while. I worked out, through doing a lot of reading and deep thinking, that I mustn't allow myself to become bitter. I had to make it a point of honour to smile at other people's babies, though I felt like running away. People in a complacent Western society don't want to talk about the death of young children, so we awarded extra marks to those of our friends who did talk about it, and top marks to those who didn't ring and say - can we come round? - because we would have said no; but who just turned up unannounced. That showed true insight and generosity of feeling.'

'And of course,' says Cannadine, 'the other thing that mattered was work. Sherlock Holmes says: 'Work is the best antidote to sorrow.' You need that reassurance that life goes on. Yet because grieving is hard work, we both felt the most uncharacteristic lethargy.'

Colley found that although she did a lot of writing, she had to throw much of it away. 'My creativity was dammed by grief. I felt no generosity, no warmth, no power of thought. Even so, had I been a traditional home-maker, without the distraction of writing and teaching, I think I would have gone mad. In the aftermath we read a lot of books about what happened, other people's experience of cot death. One said it will take three years to recover your equilibrium: and that's what we have found.'

Three years and more have passed since Harriet's death, and her parents are working at full throttle again. Each will have a book published next month. Colley's is a study of the welding of the English, Scottish and Welsh nations into Britons; a book written with such gusto and verve that even a non-academic reader drives through its pages with ease. One chapter is called Womanpower. I was curious to know whether this reflected America's greater awareness of the role of women in history.

'Yes. My consciousness was certainly raised with regard to women. In America, women's studies are much more established. Since I wanted to write about how people came to define themselves as British, it would have made no sense to leave out the 51 per cent of the population that was female. I think my having been at an American university for the past 10 years has shaped a lot of the book.'

Cannadine agrees: 'You get a quite different perspective on British history from the other side of the Atlantic. It has a liberating and stimulating effect. It makes you question, rather than just explain. We both have to teach our own history as though it were the history of a foreign country: a very different enterprise. We have both gained a lot from the freedom conferred by distance.'

They remain, I suggest, quintessentially English. Almost the first thing they told me was that they were both 'lower middle class' - not a statement an American would make. Cannadine agrees: 'They simply wouldn't understand what the category meant. In America people generally don't care who your ancestors are, and that gives a captivating kind of openness.'

'Yes,' says Colley, 'I like the fact that nobody can place me by my accent, whereas when I lived in Cambridge it was very clear that I came from the North. I was never conscious of it as a disadvantage - Oxbridge is much better now than it was between the wars - but by moving to a new country one loses a lot of the encumbrances one carries around here. There's also none of the contempt directed in England against intellectuals - as in the term 'chattering classes' - which tries to minimise the significance of people who think and discuss things.'

Nevertheless it is to the high skies and flat, green fields of Norfolk that they retreat each summer for three months to write, talk, and spend time together. They enjoy the usual gentle country pursuits: browsing in second-hand book shops, hunting through antique shops for old plates to add to Cannadine's collection; going round churches, Pevsner in hand . . . what Cannadine unashamedly calls 'rural peace and quiet and quaintness'.

The top room of the house, the attic, which is Colley's study, overlooks a roofscape straight out of The Tailor of Gloucester, with higgledy-piggledy red tiled roofs and little zig-zag streets. It is all very English.

Do they read work in progress out loud in the evenings, swap theories, influence each other? 'We're not like the Webbs . . . we couldn't collaborate,' says Colley. 'Yes, we talk about ideas and interpretations, but we have separate studies and I can't imagine us working opposite one another.'

'Linda's primarily a historian of the 18th century,' Cannadine points out. 'I'm a late- 19th-century specialist. It means we coincide, if at all, around 1800 for a few years, roughly until the accession of Queen Victoria.'

'1837,' I say automatically.

'Right. Born 1819; died 1901. A long life.'

(Photograph omitted)