'WE NO longer have to accept this stereotype of the ageing, superfluous, middle-aged woman - thanks to good old HRT. There is this new phenomenon of the exciting fifties, and I don't see why we should any longer be bowed down by the thought that we're past it and settle down to ageing gracefully. I don't think older women lack positive attributes, any more than men do. I do realise I'm talking about only a tiny minority of privileged women, however, and this is not true for everyone.

'I think I'm very lucky in being the first generation of women in their fifties who have a real, conscious sense of energised liberation in their lives. We came through the child-rearing at an early age, and are now given the opportunities to work at a time when one has enormous energy, a great feeling of security and confidence, and none of the problems of Brownies or swimming or lost gym-shoes.'

Now aged 52, Margaret Jay looks at ease in her clothes and her skin. Newly created Lady Jay, the former wife of Peter, nee Margaret Callaghan, daughter of James, has blossomed in her own right into the very modern model of a working Baroness. She was ennobled in the last Honours List to become one of Labour's 'working peers'. This is not, she insists, a reward for her 4 1/2 -year tenure as director of the National Aids Trust, or for her many other involvements in social policy. It is part of the attempt to infuse the ageing, masculine, right-wing House of Lords with fresh blood.

Commanding in height, patrician in manners, measured and discreet in all her pronouncements, Lady Jay looks and sounds like the sort of grande dame (though she would hate to be called that) who would have run a field hospital in France during the First World War, or the Waterloo Station canteen in the second. But, this being the Nineties, she leads on the battleground of sex education.

Yet she has a surprisingly colourful past and, the gossips say, a colourful present, but - thanks no doubt to her training as a journalist - she is not to be drawn on these matters.

She has never discussed her affair with Carl Bernstein, the Washington Post star journalist, which occurred in the late Seventies when her husband was British ambassador there. Bernstein's scorned wife, Nora Ephron, on the other hand, took revenge by writing a roman a clef based on the incident, in which the 'other woman' is described thus: 'A fairly tall person with a neck as long as an arm and a nose as long as a thumb and you should see her legs, never mind her feet, which are sort of splayed.' When she in turn became the scorned wife and their nanny claimed that Peter Jay was the father of her son, once again Margaret Jay kept her own counsel. Yet she is the opposite of prudish, and will talk frankly and freely about Aids and sex and the risks inherent in both, about homo- and heterosexuality, without evasions or euphemisms.

All her life she has been a left-winger and a rebel, an iconoclast and a realist, able to look on the blackest side of life. Her job on the National Aids Trust is a case in point. 'I do have a kind of imaginative chromosome missing,' she says. 'I'm good at being detached about things, even when saddened or made miserable by individual stories, I always saw the problem itself as the crucial thing. I met a lot of very young people who were HIV-positive, but I never came home and thought, 'I can't go on'.'

She hates September, partly because she has just come back from a blissful month spent in her house in Co Cork. 'This summer was the first time that none of the children were with me in Ireland, and I was quite alarmed at the prospect of being alone in this family holiday house where we've always spent time together; but in fact, I found it extremely nice to be able to do precisely what I wanted.'

She also hates this month because it reminds her of school. She attended Blackheath High School, an academically admirable, if rather conventional, girls' public school . They played lacrosse and wore gym tunics and knee socks (unusual even in the Fifties), which must have looked absurd and felt worse on an adolescent girl nearly 6ft tall.

'I hated being at school; I was very rebellious. I was the only girl who'd been in the Sixth Form without being a prefect, and I regarded that as a badge of honour. I almost saw it as a way of getting back at the school, to do very well in exams. This all-girls' school kept me a child until I was 16 or 17, unlike so many of today's children, who have lost all innocence by the time they're 10. I had one younger brother, so I was remarkably pushed into the deep end when I went up to Somerville. At 18, I was still a totally nave schoolgirl, and Oxford was my leap into adulthood.

'I was part of that rather glittering generation of people all of whose names are endlessly appearing to this day: David Dimbleby, Esther Rantzen, Richard Ingrams, Paul Foot - I come across them all the time. It's like the Rolling Stones: they keep coming back, these people who edited the university magazines and were presidents of the union.

'At that time - I went up in 1958 - the men had done National Service. They seemed so much older because of those two years' extra experience.'

Margaret Callaghan and Peter Jay were, as I remember them at Oxford, soon inseparable. They were a, if not the, glittering couple: each the child of a prominent politician, both tall, reputedly brilliant, apparently confident and sophisticated; they seemed in danger, by the time they came down in the summer of 1961, of being the kind of undergraduates described as having a brilliant future behind them.

'I shared a house in the Woodstock Road in my last year with three other girls.' Behind that innocuous remark lies the fact that in the late Fifties, women at Oxford were still quite restricted as far as contact with men was concerned, and were locked into - or out of - their colleges after 11.30 pm. The liberated life of Margaret Callaghan and the three glamorous friends with whom she shared digs was described in a rather bad novel written by one of them, Caroline Seebohm, called The Last Romantics. In her barely fictionalised version of their Woodstock Road days, Seebohm wrote: 'Our afternoon salons became famous, but our desirability lay also in the novelty of visiting four undergraduettes in almost total freedom from proctorial jurisdiction . . . so our guests, liberated from their own historic chambers, could forget their responsibility to thousands of generations of scholars and behave like normal cads and rapists.'

Nevertheless, Margaret goes on, 'We got engaged in those far-off days, and in the course of the next year after coming down all four of us got married. It wasn't acceptable just to set up house with somebody. I got married that summer of 1961, but of those four, only one marriage has survived.'

We discuss the phenomenon of the clever, ambitious graduate who decides to carve out a career and a mortgage before marriage, and discovers sometime in her thirties that a husband is more elusive than she had expected. 'Yes, that mid-thirties crisis is a really tough moment: 'Do I want a child enough to have it with this person, or even to go out and find a father for it?' For all the difficulties and problems and miseries of those of us who married very early, they seem to me less than those faced with making that calculated decision at 40: to say nothing of the fact that a late single parent offers a childhood that is definitely worse. I have a particular prejudice against the preciousness of late parenthood: that extraordinary focus on the child that goes with continuing your career and engaging a full- time nanny. I'm very glad that I'm my age and have three grown-up children, and none of that angst of having to decide on a rational basis the appropriate moment to halt in my career. My own daughter and several of her friends have married young, so maybe that pendulum is swinging back.

'There is also a sense in which those of us who are divorced are fortunate. You may not have the support, the partnership; but you don't have the . . .' she hesitates, decides not to specify, and goes on smoothly, '. . . the disadvantages, and you don't have to worry about providing domestic back-up, or considering anyone else. I'm aware that it does make you selfish; though I think that, as women, it's deeply programmed in us to worry about being self-indulgent. There is still a sense in which you feel, 'this is a treat]' '

So she doesn't find living alone difficult? (It is rumoured that she would like to remarry and looking at her - poised, calm, smooth- skinned and dark-eyed - it is surprising that she has not.) 'It would be nice sometimes for there to be a partner around, but I've survived for however long I've been on my own: 10 years or whatever it is.

'Although Peter has remarried, with three young children, we maintain a very good relationship. It certainly makes my life much easier that we're not at daggers drawn, and the concerns for our children are still shared. We ring each other constantly with the latest news and there is a tribal connection with me seeing his sister and knowing his mother, and I'm very happy about that. I've never been unhappy enough about the divorce to look back and think, I wish we hadn't done it; nor would he think that. The individual, adult relationship could not be successful; the broader social fabric of family, children and shared experiences is a separate thing.'

In October 1988, she gave up her job as a reporter on ITV's This Week for a three-year stint as director of the National Aids Trust. She extended that by a further 18 months, and felt by then that she had done enough. 'They would have liked me to stay longer, but I felt the organisation and the subject needed another five-year development programme, so I would have had to make a long commitment.

'There were other things I wanted to be involved with in the field of health education. It's extraordinary that, in our rich society, so many people live in dreadful circumstances and yet there is such a lack of anger. Also, in a sense, one goes slightly stale. At first the job was interesting and exciting and stimulating, but I was beginning to run out of steam. It needed fresh people and fresh thoughts.'

Is Aids, I ask, one reason why the pendulum is swinging back towards earlier marriages? 'I wish I thought public education had got through to that extent: my concern is that it hasn't. One of my worries is that we're not straight and upfront and even brutal about the hazards of sex in an HIV-ridden world.

'It's essential that we give young children proper preparation for life: there is a balance one can strike between maintaining an innocence and a genuine childhood in a world in which they face not simply the threat of HIV but also that of drugs, from which our generation was protected. I'm very worried about the failure of people in this country to have that debate, about how much should be formally taught at school and how much can be taught by parents. The argument gets bogged down in a sloganised debate about 'challenging family values'. We need to be much more honest about the kind of world we live in, and not view those who don't share our opinions as either wild radicals or deeply reactionary. So many people still leave school completely unprepared to take control of their own sex lives, and no language in which to talk about it. People need to be prepared to talk about these things in an uninhibited way.

'I feel my own children grew up just in time and I'm very glad they're the ages they are and not 13, 14 or 15. It's not just a matter of what's happening in discos and the backs of cars but the greater variety of hazards. We don't seem to be doing anything adequate to protect children from sex abuse. Is it better or worse than the world in which we grew up? Can one create oases of protection in an unprotected world?'

And now? What next for Lady Jay, ex-ambassadress, ex-journalist, ex-Aids campaigner, ex-wife? 'I genuinely don't have ambitions. At turning points in my life various interesting things have come my way. I've never really had a well-organised career plan in my head or in my heart.' Ah yes, her heart? 'I'm perfectly confident about this phase of my life; less sure that in another 10 years I shall be actively involved in a career. By then one might look for the loving companionship, not necessarily of marriage but of partnership . . . so this is a kind of interim phase.' That is as close to a hint as Margaret Jay will get.

This is the last of Angela Lambert's current series of Tuesday interviews. Hunter Davies will resume his interviews next week. Angela Lambert's new novel, 'A Rather English Marriage', is published by Hamish Hamilton on 12 October.

(Photograph omitted)