The perspicuous Lord Acton once wrote: "The living do not give up their secrets with the candour of the dead." Biography is an exercise in the candour of the dead - and the living. There is a lot of it about. This is a great age of "life-writing", to use the more modish designation.

Bookshops are bursting at the seams with lives of every size, shape and savour. Joseph Stalin vies with Jamie Oliver for shelf-space. And not only the famous or infamous, the important or self-important: anyone can get a life, it seems, or a ghostwritten good story.

Biography has been democratised. Some would say it has been cheapened, or devalued, in the process. The "shilling life" has become the latter-day penny dreadful. However that may be, the product has broken the bounds of the traditional categories: literary biography, military biography, political biography - all these have been outbid by celebrity biography.

Autobiography has followed suit. As with other products, placement is all. Some years ago, in a bookshop in New Orleans, I stumbled on a section labelled "True Crime and Rascality", full of the autobiographies of cops and robbers alike, many prominent in their field.

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Categories are tricky concepts. The distinction between politics and celebrity (or rascality) has worn rather thin. How are we to construe Cherie Blair's Speaking for Myself, or John Prescott's Prezza, My Story, or Lord Levy's A Question of Honour (subtitled, lip-smackingly, "Inside New Labour and the true story of the cash for peerages scandal")?

With certain notable exceptions, memoirs have gone downmarket. Rollicking, if not frolicking, is the order of the day. Reflection - the examined life - is at a premium. Twenty years ago, Lord Carrington published his memoirs, entitled Reflect on Things Past. It is a civilised and serious work. It dishes no dirt. A generation on, the author appears as a political dinosaur from a dynasty of dinosaurs; the title or injunction, at once fustian and Proustian, almost other-worldly. Today, no politician would contemplate such a title. No publisher would condone it. It is too prim, too patrician, too past - not to say passe.

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If "memoirs" suggests a work deeply pondered, carefully crafted, highly wrought - like the memoirs of Siegfried Sassoon or Casanova - not merely literate but learned, not only meditative but instructive, then in the political sphere a long tradition is in danger of extinction.

Instant autobiography, like instant history, seldom offers much in the way of edification. It is written fast - confected - for a purpose. The purpose is nothing if not transparent: to get rich or to get even. It is designed to make an immediate impact, a little like an advertisement; it is, in fact, a self-advertisement.

Memoirs, by contrast, are more self-fashioning than self-advertising. They have designs on posterity. They are made to last; to appeal to discriminating readers such as you and I; to colour our thoughts and colonise our footnotes. Classically, memoirs are part of the culture. From this perspective, "Prezza's memoirs" are little more than a contradiction in terms.

To investigate these goings-on, we at the University of Nottingham decided to offer a course on political biography. The occasion for this decision was the election of Ion Trewin to a special professorship in the School of Politics and International Relations. Special professor is Nottspeak for visiting professor.

Trewin is a distinguished editor and publisher, latterly editor-in-chief at Weidenfeld & Nicolson, where he was responsible for publishing many of the works on the reading list. He is a figure in Britain's literary life - administrator of the Man Booker Prize - and now also a biographer. After personally editing the diaries of Alan Clark, he is working on the authorised biography of that maverick Tory truth-teller, Thatcher idolater, animal-rights campaigner, military historian manque, cad, bounder and roue. Trewin is a bookman of capacious humanity - a rare bird. When it comes to biography, he is a true professional.

Ion and I agreed to join forces and teach the course together. We would present ourselves, shamelessly, as practising biographers. We would teach as scholar-practitioners. (At last a practitioner! Would this do the trick with the neighbours, who seem to think I'm unemployed? Probably not.)

We would introduce an element of creative writing into the dogged discipline of social science. This was exciting. At the same time, come the day, I think we were each a little apprehensive. Ion had never taught before; and I had never taught with Ion. Indeed, in nearly 30 years of teaching of various kinds, I had hardly ever taught with anyone. Teaching is a solitary vice.

In traditional university teaching, in particular, the seminar room is sacrosanct. Co-teaching or team-teaching, strictly defined, is rather an aberration. Lecturers lecture; professors profess. The dominant mode is readily apparent. If teaching is transmission, we privilege sending over receiving. We are not accustomed to the call and response of serious conversation. Very rarely do we teach together, interacting, interjecting, improvising, freely, without ceremony, right there, in the moment.

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Teaching in tandem, therefore, would be a new experience. What would it be like? Our double act was almost entirely unrehearsed. Would it work? Would we know? What would we do if - heaven forbid - things went wrong? The course is for third-year undergraduates; they make their choice from the menu on offer. In principle, they are volunteers. They should be willing to do some work. We determined to run the weekly meeting as a two-hour seminar. No lectures. No speeches. No presentations. Discussion based on preparation. Student-led learning. Less professing, more facilitating. High ideals. Low cunning.

The seminar is a kind of arena. If it is to be genuinely interactive, responsive, creative, the proceedings are unpredictable, the outcome uncertain. In the thick of it, even for old hands, it is hard to know how the participants will respond, what the atmosphere will be like, which direction it will take, where exactly it will end up. Such is the joy of the seminar, and sometimes the frustration.

Sharing that experience is easier said than done. Co-teaching, even co-facilitating, requires a certain sensitivity, a certain sympathy, perhaps, that is difficult to fake and equally difficult to conjure. In other words, it requires an element of mutual understanding, which in turn implies prior acquaintance.

Ion and I had been acquainted for some time - he had published two of my books; we had become friends. I felt that we understood each other reasonably well. I also felt that he could be relied upon, and that he would be a sympathetic presence in the classroom. But I could not be sure; and neither could he. We had seen little enough of each other over long periods. Our relationship had been established in roles familiar to us (author, editor). Here we were venturing into the unknown, in the words of T.S. Eliot:

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... And so each venture
Is a new beginning, a raid on the inarticulate
With shabby equipment always deteriorating
In the general mess of imprecision of feeling,
Undisciplined squads of emotion ...

All of this fed our insecurities. Mine focused conveniently (and contradictorily) on others. Suppose Ion talked too much. Or didn't talk at all. Suppose we disagreed. Or couldn't find anything to disagree about. Suppose the students didn't take to him. Or took to him too much. Suppose they acted up. Or (more likely) went to sleep. What would Ion think?

All shall be well, as Eliot says, and all manner of thing shall be well. In our case, fortunately, all manner of thing turned out extremely well. The course was oversubscribed. Two seminar groups were formed, with about 20 students in each. So two performances a week, comparing notes in between: predictably, perhaps, the dynamic of each group often seemed quite different.

At the first meeting we got them all to write their autobiography (in 20 minutes), and then to swap, to see what kind of lives they had thought to record. Taken by surprise, they were hooked. A few wriggled off, of course, over the next few weeks; but for the most part they maintained their interest, and produced some excellent work, several remarking (perhaps ruefully) that they had done more for this module than they had ever done before.

For their first piece of coursework they had the option of writing a forward obituary of Tony Blair, as if for "the morgue" of a quality newspaper (several were so forward as to finish him off entirely, in a variety of imaginative ways, the best involving a measure of poetic justice); or a dictionary of national biography-style entry on a non-British person of their choice. The Oxford Dictionary of National Biography, or DNB, proved to be an invaluable resource. Readily available online (oxforddnb.com), and easily searchable, it is a mine of mini-biographies, often written by maxi-biographers, generating some intriguing pairings - Douglas Hurd on Alec Douglas-É«ºÐÖ±²¥, Roy Jenkins on Harold Wilson. For our purposes, moreover, the very idea of "national" biography is an interesting one.

The DNB itself is something of an institution, and Britain is often said to have a kind of comparative advantage (or morbid interest) in the genre. Is there a "British way" in biography, as has been claimed for warfare, by comparison with, say, an American way? Food for thought for the students' research papers.

The seminars typically evolved into small-group work (some four or five students), punctuated by bouts of plenary summary or round-table discussion. Each week the conversation focused on a series of tasks given out the week before. Everyone was expected to come prepared. For a session on the DNB, for example, the tasks were as follows:

1. Access the DNB online. Sample some entries. You will see that they follow a certain format. What is the format?

2. Read the entries on recent prime ministers (Churchill, Attlee, Eden, Macmillan, Douglas-É«ºÐÖ±²¥, Wilson). Where they have been revised, compare the different versions (click on "Archive" on the respective entries). How have they changed? Has there been a reassessment? What kind?

3. Comparing the current versions, what conclusions can you draw about the historical significance and relative standing of these PMs? How has posterity treated them, so far, according to the DNB?

4. How candid are these entries? How much do we learn about the private life rather than the public one? The inner life rather than the outer one? About personality and character?

While the students grouped, Ion and I would often let them alone for a while, and then each of us would set out on a tour of the groups, sitting in, listening, prodding, encouraging, inciting; sometimes answering questions; doing our best not to dominate. I believe that the best work may be done in these small groups, where they reach a kind of intellectual boiling point and begin to discover things they did not know they knew.

To enrich the mix, we took the students on a visit to the National Portrait Gallery in London. Here, with the aid of a scintillating introduction from the director, Sandy Nairne, we concentrated on portraits of prime ministers, beginning with John Singer Sargent's magnificent portrait of Arthur Balfour ("a portrait of a philosopher and a statesman - a sad philosopher and a sad statesman", wrote G.K. Chesterton), through Yousuf Karsh's bulldog Churchill to Helmut Newton's riveting image of Margaret Thatcher in supremacist mode, facing down the photographer and the world.

In sum, the experiment seemed to work. It will be repeated this year. Teaching in tandem was a marvellous experience. The students benefited in all sorts of ways from Ion's presence, nowhere better demonstrated than in his counsel and his contacts. One lost soul researching prime ministers' press secretaries was put in touch with Alastair Campbell and Bernard Ingham. Campbell promptly rang her on her mobile. That is perhaps the very definition of a special professor.

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