They say tacky, I say phooey: Maeve Haran, the best-selling author, defends her craft against literary establishment sneering

TONIGHT, in the elevated surroundings of the Royal National Theatre I will be taking part in round 29 of the debate that won't go away: is the blockbuster high art or lowest common denominator? What's intriguing is why this fight rages on and on, fuelled, it sometimes seems, by a fascination on behalf of the literary establishment with a form it affects to despise.

And there is undoubted disapproval of the bestseller from lit-crit quarters, shown not just by the absence of bestsellers from the Booker shortlist (where no one would really expect to find them), but also by the dismissive tone of reviewers, or by the simple lack of reviews of most of the books that make up 80 per cent of the paperback bestseller lists. A blockbuster, so the suspicion goes, is a nasty tacky thing that any fool could write, given two weeks off work and an Apple Mac. Just choose the genre, work out a formula and there you go. Megabucks and movie rights.

This is a delusion I once shared. Five years ago I gave up my job, nipped in to WH Smith and scooped up an armful of gold-blocked one- word titles. I proceeded to analyse them in search of the key to the genre then known as 'sex 'n' shopping'. I followed this process with great diligence and precision, working out exactly how many bonks, guilty secrets and lovers who turned out to be the heroine's father were needed per book. It never occurred to me that a mother of two small children who had forgotten what sex was and always shopped in Marks & Spencer might not be the ideal candidate to write a sex 'n' shopping masterpiece.

After six months I sent off outline plus sample chapters (just as it tells you in the handbooks) to an agent and waited for the offers to flood in.

The eventual feedback made me wish I'd hung on to the day job. It was, said my agent, formulaic, dull and passionless. What was more, the genre I had navely adopted was already dead on its feet.

It was only when I chucked away the formula and wrote passionately about a subject that really interested me (the attempt to balance career and motherhood) that the bestseller lists beckoned. By following my own preoccupations I'd hit upon a theme that preoccupied thousands of others, and Having It All's sales reflected that.

I have to admit to great surprise at the novel's dramatic success. I honestly feared that the theme was too limited for that kind of mass appeal. In retrospect I shouldn't have been surprised. Commercial novels have often been first to pick up on changing social mores - written, as they so often are, for women by women. Even the sex 'n' shopping format provided an insight into social change in its early days. Its women-on-top heroines, wallowing in newly discovered power and sex, heralded a new self-image for women which might have been largely fantasy but certainly marked a change of tone from the woman-as-domestic-victim novels that had gone before. And the current vogue for the Aga-saga, with its concentration on English rural life, may reflect the phenomenon of 'burrowing' highlighted by marketing gurus as the Nineties reaction to Eighties materialism.

While few bestsellers are actually written to a formula, they do, nevertheless, have certain characteristics in common. Most popular books reflect the author's voice (that odd blend of personality, observation and style that marks out a Cooper or a Binchy or a Cookson); they are strong on drama and storytelling; and they are often optimistic. I always know how I want my novels to end before I start. Endings are, to me at least, what a really good read is all about.

A recent criticism of my new novel, It Takes Two, admitted that while I might understand the substantial concerns of my readers I had nevertheless written the literary equivalent of a 'feelgood' Hollywood movie. Well, fine, I don't object to that. The 'feelgood' criticism was also levelled at Nora Ephron's recent hit, Sleepless in Seattle. And what's good enough for Nora Ephron is good enough for me.

The encouraging thing about bestsellers is precisely that they aren't predictable. Publishers spend hundreds of thousands of pounds in advances, trying to keep their fingers on the commercial pulse. And then, apparently out of nowhere, comes an unsophisticated story of duty and sacrifice, in which a married woman in rural Iowa meets the love of her life but decides to give him up for the sake of her husband and children. And The Bridges of Madison County sells 4.3 million copies (in hardback]) to a United States where divorce rates are soaring and serial marriage is the norm.

Where publishers do seem to go wrong (just as Hollywood studios do) is by rushing into print with carbon copies of that unexpected hit. Thus everywhere you look in bookshops the watercolour-drenched Aga-saga threatens to drown you, or Grisham-esque greeny-grey lettering announces the latest legal thriller.

There are signs, however, that the blockbuster novel is being taken seriously, if not by critics then by potential writers. I shared a platform on air the other day with Malcolm Bradbury (ardent defender of the literary novel). He pointed out that while half the intake of his sought-after creative writing course at East Anglia wanted to write for the Booker, the other half now wanted to write bestsellers. What's more, he conceded, it was far harder to teach them to write the latter. Maybe this is true: despite the plethora of How To books that offer advice on writing your very own blockbuster, the number that make it is surprisingly constant.

There is one other encouraging development from the literary front line. While we argue away in this eternal War Between the Genres, someone has quietly managed to tune into the concerns of the moment, write a gripping bestseller and win the Booker prize. His name is Roddy Doyle.

Maeve Haran's latest novel, 'It Takes Two', was published on 13 June by Michael Joseph ( pounds 14.99). The Royal National Theatre debate, The Culture of the Bestseller, is tonight at 6pm in the Cottesloe Theatre, tickets pounds 3.50.

(Photograph omitted)