My observations over a number of years have led me to conclude that Lisa Jardine CBE, the long-standing Centenary Professor of Renaissance Studies at Queen Mary, University of London and the newly appointed chair of the Human Fertilisation and Embryology Authority, is incorrigibly two-faced.

Portrait of Lisa Jardine by Des WillieOn most occasions only one of these faces is visible. This is her strictly sociable persona, which features a broad, engaging bright-eyed smile and a capacity for enthusiastic, funny, observant small talk about the exigencies of everyday life (the advantages of being old enough to have a London Freedom pass, the interminable nature of academic committee meetings), which ensure that she is the happy centre of attention at any function she chooses to attend.

But watch closely and you'll see that rather a different face appears at those moments when a guest makes a remark which ever so slightly wanders into political or academic territory. The bright-eyed smile remains intact but now it is accompanied by a slight but observable tightening of the lips which signals that Professor Jardine is about to take matters seriously, very seriously indeed.

Those who've not seen Lisa Jardine in this mode can sometimes make the mistake of over-emphasising the sociable side of her personality, can even conclude that she is, as one sociologist put it to me, really far too extravert and outgoing to be "a proper academic". Critics of this kind can only find extra ammunition for their view in her recent readiness to turn her sociable thoughts about life into a very popular and beautifully crafted series of Point of View talks for Radio Four.

It is probably a matter of gender. We seem far more ready to allow that men are capable of combining good humour and extreme sociability with high intelligence. Stephen Fry's acumen is hardly undermined by his readiness to play silly games with Alan Davies on QI, but when women manifest both traits we are inclined to devalue the latter. It does seem an unreasonably high price to pay for being a nice person.

All of which meant that although I was flattered by the cheery readiness with which Lisa Jardine agreed to this interview, by her insistence that it would be an absolute pleasure, I made sure to arrive on time and get quickly down to real, tight-lipped, intelligent business.

There was an obvious starting point. Several years ago when I was teaching at the University of York I'd become fascinated by some of the work being carried out by academics who'd started calling themselves "sociologists of science". There were many strands within this new sub-discipline but one central concern was a devaluation of the idea that "science" was a special domain of knowledge which was not contaminated, as were other epistemological fields, by social norms and conventions and expectations. Such an approach not only subverted the popular notion of scientific discovery as a "eureka moment" but also laid waste to the idea of the solitary scientific genius.

It is perhaps further evidence of the insularity of disciplines in British academic that none of the work I'd read in the sociology of science had ever credited the research that Lisa Jardine had been carrying out into just such matters for several decades.

Not that she or the sociologists of science seemed to have had much effect upon the popular idea of "scientific genius". Did Lisa Jardine have any explanation for the persistence of the idea?

"It's a terribly potent myth. When you talk to audiences, to the so-called general public, you find that they desperately want to cling to the idea of isolated geniuses. It gives you a genealogy to hold on to. Newton begat Einstein and so on. It gives linearity to the growth of knowledge and the growth of civilisation. It fits the narrative story-telling which is so highly valued. There's a long tradition in the west of representing innovative thought as emanating from a great mind. It all hinges around the great pre-Enlightenment voice of Descartes, the 'I', the first-person 'I'. And that in turn tempts the historian of ideas into valorising that first person. If you're going to debunk that notion then the starting point is an absolute refusal to place boundaries between science and engineering and technology. That's a boundary that someone like developmental biologist Lewis Wolpert wants firmly in place. He wants to say that science is special. That science is a place where everything happens differently and it happens in the mind of a very different kind of individual. No."

Anyone who wants an example of how effectively Lisa Jardine debunks the myth of the pure scientist need only turn to her meticulously researched biography of the 17th-century maverick Robert Hooke. Hooke was certainly a successful scientist but he was also an architect and surveyor (he helped Wren rebuild London after the Great Fire of 1666) and an engineer who designed a wide range of measuring instruments. This wasn't a peripheral interest, it was central to the development of science.

"There can be no science without precision. And this practical concern with measurement which predates modern science was in the hands of clockmakers and balance-makers who had engineering and practical backgrounds. So already we're into the social sciences, because all of these people are perfectly happy that their activities are what Francis Bacon called 'deeply enmeshed in matter'. Every innovation they produce is a direct result of social pressures upon them, often military pressures, to produce a particular solution. So by refusing, as I do, to separate Hooke the scientist from Hooke the skilled lens grinder, Hooke the surveyor, Hooke the microscopist, we're already out of the realm of the unique genius. And incidentally it's about time that someone wrote about Newton that way. I'm really bored with Newton being cited as the great counter-example. Because he wasn't."

Portrait of Lisa Jardine by Des WillieLisa Jardine certainly annoyed a number of prominent scientists with her debunking of the stand-alone genius, but it's a mark of her capacity for hard, detailed research, and of her readiness to take on established truths, that she then confronted the myth of the pure artist, the inspired beings who according to conventional art history painted because they were consumed by a desire to express transcendent truths. In Worldly Goods, she shows that the real impetus for the production of Renaissance art, for this amazing flourish of creativity, was sheer material consumerism.

I suggest to her that it was the same sort of dissatisfaction with compartmentalisation, with keeping the scientist and artist immunised from their surroundings, that informed Going Dutch, her recent study of the intellectual, artistic and political connections between Holland and England in the 17th century. What she was debunking here was the myth of the solitary nation, the idea that there was something immanent about the development of England and Englishness.

"Maybe this concern with context has something to do with my own intellectual life." She can readily cite biographical reasons for such eclecticism. Neither her father, the distinguished mathematician and "intellectual democrat" Jacob Bronowski, nor her mother, Rita, an artist and cultural entrepreneur, ever kept knowledge in boxes. They ranged as readily across science as they did across the arts. But Lisa has a more contemporary explanation for her refusal to reside in disciplinary pigeonholes.

"I spend the whole time juggling - no, not juggling; I spend the whole time interleaving the various aspects of my life. Maybe women can do that more. I cooked a quiche while I was waiting for you. And before that I went to a meeting. Now I'm talking to you about what I believe. And they're all actually related. They don't belong in separate parts of my brain. They bleed into each other. They defy the fictions of separation. You can take it at almost a physiological level. When I was having chemotherapy, I was teaching all the time, to take my mind off what was happening. It was absurd because I often couldn't remember the last sentence I had spoken. And two graduate students who are particularly dear to me got into the habit of prompting me. Just like on stage. So I went to my oncologist and said, I'm having a terrible time. The chemotherapy has affected my brain. No, she says. No, it doesn't get into the brain. She seemed to have to believe that there some sanctified area called brain which was safe from the poisons. Another sanctified separation."

As we talk I realise that Lisa displays another distinctive characteristic when she's in full academic mode. Whereas her social conversation rattles happily along, when she's talking about matters of the mind she quite frequently pauses for several moments to reflect, or goes back on herself to correct a loose turn of phrase, an inelegant formulation. She picks her words especially carefully when I suggest that those who talk about science as a distinctive domain also have a tendency to talk about science as "truth", to counterpose it, in the manner of Richard Dawkins to the non-truths of religion.

"My mantra is that science is about doubt. Science is all about nudging up towards what you hope is the truth. Science, unlike religion, makes no fundamental claims that you simply have to believe. Even something like the second law of thermodynamics is always bracketed. I think there are comparatively few people like Dawkins who are capable of sustaining a lifelong conviction that there is no God. I think most of us, and I include myself, have no clear idea. We're still in a state of uncertainty."

But wouldn't Dawkins say that was something of a cop-out? He'd not let anyone get away with such uncertainty. He'd ask them to produce some evidence for God's existence, suggest that their feelings and thoughts and occasional sense of transcendence didn't amount to anything we'd recognise in any other area of life as evidence. Wouldn't you want to challenge believers in similar ways?

"No, I don't challenge them there. Where I challenge them is when they tell me that it is wicked to do things because religion says so. But I need there to be a pressing reason for rebutting someone's religious beliefs. In my youth I'd have been much more aggressive about this. I hate to harp on about it but I had a watershed recently when I was ill. It's bloody hard to be dangerously ill and not have a comforting belief. If you think you might die next week and you know that you don't believe and that getting a priest or a rabbi or a clergyman won't make the slightest bit of difference either now or in the hereafter, that's a very lonely and exposed place to be. Before I had experienced my own mortality, I was extremely impatient with people who took that position."

But there were still points at which she'd confront religion?

"Oh, yes. When some member of the House of Lords stands up and says IVF is against God's will and the legislation should not allow it, then I'm prepared to go hammer and tongs because I believe they have no right to make that general claim. No right at all. They have an absolute right to say it to their congregations, to their constituents, but they have no right to perpetrate it as a universal philosophy."

It was not suprising to find Lisa Jardine selecting IVF as the issue which might arouse her wrath. It's only a few weeks since she took over the chair of the Human Fertilisation and Embryology Authority and she is already gearing up for some of the fights that lie ahead. Many of these battles would surely be quite unlike the standard academic arguments in which she'd been involved in, that they raise complex questions of morality, matters of conscience?

Portrait of Lisa Jardine by Des WillieShe swatted that concern away. "Conscience seems to me to be a cover word for dogma. I'm not anti-Catholic, by the way, as opposed to any other religion. I'm uniformly anti-religion. Not parti pris or partisan. But the noise the Catholics made. Just ask yourself for a second. Under 10 per cent of this country even admits to being Catholic and what percentage of them took this extreme position [about the sanctity of the embryo]? How many of them don't use contraception for instance? And are we ready to believe that these [Catholics] in privileged positions can speak on matters of conscience for the whole population? I don't think so."

But even if that was conceded, wasn't she still up against what one might call the common morality, the sense among ordinary people that some of the work scientists were now doing was interfering with nature? Such views might be scientifically irrational but they could be deeply held enough to restrict future research. Despite all your appeals to evidence and to the possible medical benefits which might accrue, the general public might still say "no".

"Well, would they? That's my first question. Or does the Daily Mail tell us they'd say 'no'? I did a radio programme during the progress of the recent Embryology Bill through Parliament and I was ready for some mischief. And yes, they had put together this vox pop package in which they had gone into a children's park and interviewed a rainbow collection of parents. Well, I gripped the arms of my chair as this package which I hadn't heard before came on. It was topped and tailed by a jolly young reporter saying 'Everybody's really concerned'. But in between these remarks, every single one of these 20 young parents said something like 'I really think we have to do the research that's necessary' and 'I really don't have a problem with this'. Every single one. And presumably if they'd had a counter-example they'd have put it in. They'd have put it in."

Wasn't this notion that the general public would go along with the decisions of the Authority slightly optimistic? There'd surely be times when the case would have to be argued on moral grounds? When one morality might have to confront another? In those circumstances what would be her moral pitch?

"I'm strictly anti-Hobbesian. Like any social scientist I believe that humans are community animals and I think I hold the Rawlsian view that the fallback position is to ask human beings to imagine what it would be like to find themselves in the worst position they could envisage. And then see what they say. I believe that it is part of the definition of a human being that they have that capacity for ethical thought even though it may be stifled by contingencies. That's why I teach. It's only when human beings are able to have the understanding and ability to make independent reasoned judgement that they become fully moral. I want the public discussions that we [the Authority] have to be part of the human condition. I find myself in an extraordinary place, arbitrating on matters where there is no right and wrong but only a sceptical nudging towards what might be the optimal outcome, whether it is remedying the tragedy of infertility or working at the cutting edge of stem cell research which maybe in a generation can help us mitigate or even reverse the effects of illnesses like Alzheimer's or Parkinson's."

I'm aware that my time with Lisa has come to an end. Although it's very tempting I know that what I mustn't do now is switch off the tape and relapse into the form of joshing sociability which has informed our past encounters at parties and conference socials. Professor Jardine will have other engagements for which she might need to save her sociable face. She certainly won't have time for any chitter chatter about her next holidays (she's passionate about France) or about the progress of the vegetables she's planted in her roof garden (she's particularly pleased with her potatoes and tomatoes).

"Thank you", I say limply. "That was great." "Thank you," she says, "for such a stimulating talk." I nod goodbye. She gives me her special smile before turning briskly to Des the photographer. "Now, how do you want me? Actually, I always find that I look better in photographs than I do in real life." He looked charmed already.

Original photography by Des Willie