DJ Taylor: Plagiarism is the sincerest form of flattery*

<i>(*with apologies to Charles Caleb Colton, coiner of "imitation is the sincerest form of flattery")</i> Dan Brown is the latest writer to be accused of copying work of others. But just where does homage end and theft begin?

According to the profile writers, Dan Brown is a retiring kind of a guy, camera-nervous and preferring the sequestration of his New Hampshire hidey-hole to the rigours of the book tour. This, famously, is the man whose publicists always say no and is thought to have declined all interview requests for the past two years. Last week, on the other hand, mild-mannered Mr Brown had storms of unwelcome, and unavoidable, publicity descend on his head, all brought about by a summons to attend the High Court in respect of a claim by two disgruntled fellow-scriveners that his multimillion-selling theological thriller The Da Vinci Code plagiarises their work.

The case, now adjourned until Tuesday when Brown is expected to take the witness stand, refers to a piece of non-fiction first published nearly a quarter of a century ago, a considerable copy-shifter in its day, called The Holy Blood and The Holy Grail. The plaintiffs, Michael Baigent and Richard Leigh, two-thirds of a three-person writing team, not only allege that Brown's account of the encrypted messages in Leonardo Da Vinci's artwork pilfers the "central theme" and the "architectural edifice" at the heart of their own book, but that it harbours at least 15 instances of similar phrasing. Key to the row is Brown's annotated personal copy of Holy Blood: Brown maintains that the marginalia got scribbled some time after The Da Vinci Code hit the racks.

Curiously enough, Brown and his publishers, not to mention the nervous distributors of the Ron Howard film, due out in May, have been this way before. He turned up in court when a little-known writer called Lewis Perdue claimed that The Da Vinci Code pillaged material from a novel of his published back in 2000. The judge found in Brown's favour, but the case, quite as much as its successor now unwinding in central London, will have sent a little tremor of excitement coursing through the veins of a great many creative artists who have imagined themselves traduced in this way.

Plagiarism rows - such cases rarely get to court, and Brown's difficulties may be ascribed to his $200m fortune - come round as regularly as the Victorian muffin man. Only last April, for example, the novelist Hilary Mantel arrived at the Cambridge Literary Festival to find a fan enquiring if had she by chance read the recently published Rock Me Gently by a debuting memoirist called Judith Kelly? No, Mantel replied, the work had not yet come her way. Well, her informant urged, it would be a sound idea to take a look, as it bore a resemblance to her novel Fludd.

Having investigated Kelly's story of a 1950s Sussex childhood, dominated by some brutalising nuns, Mantel was able to isolate 10 passages which reproduced, in some cases almost word for word, her own efforts. Bloomsbury Publishing, to whom representations were made, lamented their author's "photographic memory". Further resemblances to Brighton Rock and Jane Eyre were noted by critics, and plans for a paperback were postponed.

Handfuls of major-league novelists, it transpires, bear scars of this kind, either in the role of accused or accuser. David Lodge ran into trouble when Nice Work, a state-of-the-nation exercise which brings together a Birmingham industrialist and a feminist academic, was thought to resemble a work of romantic fiction issued well before its 1988 publishing date.

In the late 1970s several critics dutifully observed that Ian McEwan's The Cement Garden, in which a gang of suburban children conceal their mother's corpse, seemed to derive from Julian Gloag's Our Mother's House, which McEwan claimed never to have read.

At about the same time, Martin Amis had a tremendous set-to with the American writer Jacob Epstein, whose campus novel Wild Oats (1979), he maintained, reproduced passages from The Rachel Papers, published six years before. Amis was able to quote, chapter and verse, striking images of his own coining that had mysteriously made their way into Epstein's book.

Unsurprisingly, "borrowings" of this sort are detected across the creative spectrum, a riff, a chord progression, a particular juxtaposition of light and shade. The late George Harrison ended up $1m out of pocket after the composers of The Chiffons' "He's So Fine" noted the duplication of their central melody in the ex-Beatle's "My Sweet Lord". Mid-1990s Brit Pop hopefuls Elastica suffered a similar, though less expensive, indignity at the hands of punk veterans The Stranglers.

Neutral observers, noting the length that the Brown case is expected to take, might wonder what all the fuss is about. On paper, a plagiarism claim ought to be one of the easiest things to prove in law. X produces a line of prose, a succession of chords or a song lyric; Y repeats it: what could be simpler? In fact, this is one of the greyest areas in art. A phenomenon, more to the point, turned yet more complex by the fact that anxieties over intellectual copyright are of fairly recent date.

Shakespeare, for example, constructed his plays on the magpie principle, and several 18th-century novels work as literary portmanteaus, incorporating all kinds of material that caught the author's eye along the way. Junior members of Renaissance painting dynasties would have taken it as a compliment had anyone suggested that their pictures looked like Dad's.

In this struggle to separate an aesthetic debt from straightforward larceny, everything hangs on the intentions of the plagiarist. A popularising author who chances on an abstruse work by an obscure academic, takes its themes, structures and intellectual viewpoint and sells half a million copies on the back of this expropriation has clearly stepped over the line, but what about the innocent act of homage?

To give the dilemma a personal touch, I was once accused by some hawk-eyed reviewer of abstracting a piece of figurative language from Ian McEwan. The particular image described the members of a crowd "stirring like troubled dreamers". I went and checked. McEwan had indeed used this simile in one of his early stories. All I could claim in my defence was a huge, late-adolescent fixation on McEwan's work which had clearly worked its subconscious magic on my own stuff.

In much the same way the late JL Carr once told me that to invigorate the language of A Month In The Country, which made the Booker shortlist and was filmed with Colin Firth and Kenneth Branagh, he inserted into it four sentences from a novel by his great literary hero, HE Bates. Calculated rip-off or act of homage? I don't imagine Bates's estate would have been greatly exercised.

In that wider landscape in which artists operate, the line between silent burglary and self-proclaimed emulation has been steadily erased both by aesthetic theory and commercial practice. Certain academic critics regard what the French call intertextualité (the notion that as all works necessarily borrow from each other, we ought to encourage this literary file-sharing) as a positive virtue.

"Sampling" has been a feature of the music business for more than a decade, sometimes tolerated, occasionally provoking those sampled to litigious fury (all royalties from Richard Ashcroft's Bittersweet Symphony go straight into the bank accounts of Mick Jagger and Keith Richard.) In pop, especially, an obsession with heritage goes with the territory. Sued by The Stranglers for lifting the riff from "No More Heroes", Elastica might also have expected trouble from art punks Wire, whose influence rampaged through several of their songs. Wire declined to bite, revealing that their own numbers had plagiarised many a classic from the rock canon.

As to where this leaves Dan Brown and his accusers, only the finest legal mind could say. The Holy Blood and the Holy Grail is a well-known book. It would be odd if, in his two years' research, Brown hadn't come across its theories in some form or other. But then, many a work of modern fiction is expressly constructed on the back of some earlier work. Although it reproduces none of its words, Hilary Mantel's own An Experiment in Love is a deliberate homage to Muriel Spark's The Girls of Slender Means. Reproached with abstracting the riff from The Beatles' "Taxman" for The Jam's "Start", Paul Weller replied that only a half-wit would have expected the resemblance not to be detected.

Amusingly, it will be left to Mr Justice Smith to decide a conundrum that has been puzzling literary critics for centuries: the difference between influence and theft.