Philosopher, House of Lords crossbencher, headmistress, educationalist, broadcaster, public policy pioneer, ‘Britain’s chief moral referee’, and, closer to home, former Mistress of Girton College, Baroness Warnock, now aged 90, has certainly seen a lot in her time.

Now famous as the government’s go-to woman in matters of medical ethics, Warnock’s ambitions lay in Philosophy right from the start. ‘‘I remember when I was about six asking my older brother what Philosophy was. He said, ‘well, it teaches you how to think.’ I said, ‘but I can think already.’ ‘‘But I did know from a very early age that I wanted to do Philosophy.’’

And so, off to Oxford she went. ‘‘It was a terribly exciting time to be in Oxford, because everyone adored being back after the war,” she tells me. “And our teachers had been brooding over their thoughts without being able to publish or lecture during the war years, so there were so many ideas. Our lectures were as yet unpublished books.’’ With a nostalgic laugh, she adds: ‘‘the austerity that went on was worse than during the war; we were hungrier. But it was just so exciting being so free. “I feel terribly grateful for having been an undergraduate at such a marvellous time.’’

It was in this iconoclastic, no-nonsense era of Philosophy, that she met her husband, Sir Geoffrey Warnock. He was known as “by far the most intelligent undergraduate at Oxford”, and later served as Principal of Hertford College, and as Oxford’s Vice-Chancellor. With her brother also heading a Cambridge college, as former Master of Corpus Christi, Baroness Warnock belongs to something of an Oxbridge dynasty. Discussing her term as Mistress of Girton, she states that ‘‘yes, absolutely’’ it is time for all-female colleges to admit men. Although at the start of her career such colleges had the benefit of guaranteeing that ‘‘there were bound to be at least four women philosophers, when we were very much in a minority’’, she remarks that the times have changed.

Warnock left Oxford University to take up a post as headmistress at a local girls’ high school, although she regarded this move as ‘‘a way of letting me off all the awful graduates who perpetually beleaguered me. With undergraduates, you talk to them for an hour, give them an essay, and they go away. But these graduates wouldn’t leave me alone’’. Not many headmistresses have taught themselves the French horn in order to bolster the school’s orchestra.

She was, and is, a vehement educationalist. This cause provided her entrée into public life. Finding her footing on various educational panels, she soon found herself at the helm of high-profile committees dealing with the ethics of education for disabled children, animal experimentation, and, most famously, embryology. In these capacities she precipitated the most momentous and contentious changes of the era in medical attitudes. She had long joked with her husband that she wanted to wake up and discover she had become famous; waking up after the publication of the Warnock report, which banned experimentation on embryos beyond 14 days old, she did just that.

Rightly, she regards the majority of her contribution to public policy with pride. There’s an exception, though; she tells me that the special education reforms that she led have ushered in an ‘‘appalling system.’’ The caustic pen of Melanie Phillips savaged her for this change of position, but she laughs this off. To be objectionable to Phillips is a prized distinction for any liberal.

We have certainly been, to a large extent, navigating by Warnock’s moral compass for the last thirty years. But what guides the guide? If she is our ‘moral referee’, what rulebook does she enforce?

Warnock has emphatically and publicly rejected religion as the basis of morality. She believes that morality became entrenched in religion because of human need to buttress the principles essential to coexistence. Since she sees the aspiration of law as being to reflect morality; to deny religion the status of the origin of morals is to invalidate its claim to sway in government. How, then, does she conceive of morality?

‘‘Humans are political animals; they need to live in a community,” she says. “Therefore they develop a kind of morality of how to treat one and other, and how to get over the selfish temptations to which they are all subject.’’ As she elaborates with examples from Sophocles, as well as contemporary philosophical works, I realise that she is no longer participating in an interview; she is giving a supervision. ‘‘I think the belief in Human Rights is what has replaced this belief in God-given laws. They encapsulate morality.’’

‘‘There are standards that are fairly well agreed. When we say somewhere has a poor Human rights record, we all know what is meant. We do agree to a very large extent on broad concepts of justice, and how humans should treat each other, and particularly how they should not. So that does form a kind of common moral standard.’’ She sees morality not as a relativistic concept, but as an absolute truth.

In the House of Lords, Bishops are regarded with a degree of moral reverence. They conventionally have, in a self-regulating house, the rare privilege of being allowed to speak when they wish, and without interruption. If religion confers no moral expertise, why does Warnock accept such a tradition? ‘‘I don’t think their faith gives them any particular authority,” she tells me, “but I part from them only when they try to derive their moral views from their faiths. But it is just a convention.’’

She explains the mechanics and the eccentricities of the Lords with the familiarity and affection of an old hand; she has been a member of the upper chamber for nearly three decades now. But does anything still surprise her? ‘‘The House of Lords is so despised by this government. It’s appalling to me how this government does not take it seriously; if they did, they would not keep appointing so many people to it, because it simply can’t function.

“And yet they give us such ill-prepared and poorly thought-through legislation that we’d be in a terrible state without the Lords.’’

‘‘We do need two houses, but we need the Commons to take us seriously.’’ As she nods conclusively, it is hard to imagine Warnock, at least, ever being taken otherwise.