Victor Hugo's descendants are not so much miserable as furious. It's as if a musical hack had turned out Beethoven's Tenth Symphony or some unfeeling brute had written a sequel to Jacques Brel's ' Amsterdam', they claim.

What's made them so angry is that a French journalist has written and published a sequel to Hugo's masterpiece, Les Misérables. They are taking legal action to ban the book and seek damages of Fr4.5 million (£410,000) from publishers Plon for undermining the author's moral rights, at a court hearing in Paris on 27 June - unless agreement can be reached.

Hugo's descendants say they have taken legal action, not to 'recover any part of the dirty money' the publishers and authors have made from the sequel, but to take 'a moral and symbolic' stand against what they see as the corruption of literary values by soulless global capitalism.

The author of ' Les Misérables 2', François Cérésa, has kept quiet during this row. But his lawyer Jean-Claude Zylberstein defended his client's work, saying: 'Cérésa wanted to pay homage to one element of our literary heritage. Some musical and cinematic adaptations have mauled Hugo's work more, without shocking his heirs.'

Cérésa's book, entitled Cosette, or The Time of Lost Illusions, has been published with a huge PR budget stressing its links to Hugo's original. Around each copy is a red band advertising the fact that this is intended to be a sequel to the melodramatic tale of the reformed convict Jean Valjean, unbending policeman Javert, the evil Thénardier family and little orphan Cosette.

Inside, Cérésa explores the premise that the holier-than-thou Javert - who doggedly pursues the hero Valjean in Hugo's original, only to commit suicide by jumping into the Seine at the end - does not actually die.

Javert, the author argues, is 'the real hero of Les Misérables - he is perhaps not quite as bad as one thinks. I wanted to know more about him, and I wanted the Thénardiers properly punished.'

The critics, though, have been lukewarm. Le Monde's review, for instance, had the headline: 'Un melo un peu falo' (a 'rather colourless melodrama'). But perhaps Cérésa should take heart from the fact that nineteenth-century reviewers didn't much like Hugo's original either. The reviews, as Hugo noted at the time, were 'reactionary and more or less hostile'.

None the less people stormed bookshops to buy the 48,000 copies of Les Misérables put on sale on the first day in 1862. So far Cérésa's sequel has sold 65,000 copies.

Adapting Les Misérables has regularly proved an irresistible temptation. And no wonder - it is the most read French novel in France and in the world. A television adaptation starring Gérard Depardieu, Charlotte Gainsbourg and John Malkovich was watched by 10 million viewers in France.

There have been 19 feature films adapted from the book, two television films, three television series, umpteen stage versions - not to mention the money-spinning musical.

But it is not these that have infuriated Hugo's ancestors, since they are all adaptations rather than sequels. It is the fact that someone has dared to change the original ending. 'Hugo considered Les Misérables to be a complete work that called for no sequel or rewrites,' they say.

As a result, the dispute has set in train a viperous literary row embroiling such intrigu ing issues as the moral rights of the author, freedom of expression and allegedly declining standards in the French publishing industry.

Shouldn't something be done to stop the glut of lucrative but shabby sequels to classic fiction? Where will it end? One respected French literary biographer recently feared that it might end in A la Recherche du Temps Perdu II: the Biscuit Bites Back?

Lauretta Hugo, wife of Jean, great grandson of Victor Hugo, last took action to defend what she saw as the author's honour in 1997 when Disney released the cartoon film The Hunchback of Notre Dame. She and her children, who guard Hugo's literary flame, saw this as commercial abuse. It wasn't even mentioned that the film was based on a book by Victor Hugo.

She said: 'We want to express our indignation against this threat to the integrity of a work considered to be an undeniable treasure of our universal cultural heritage.'

Hugo's descendants are particularly angry about the emergence of Cosette because next year they were hoping to celebrate the bicentenary of Hugo's birth. 'The thieves who have transformed Frollo into a judge and resuscitated Javert don't have ethical or artistic scruples: they just make products and their sole concern is to sell as many as possible,' Lauretta Hugo said.

The row has provoked a wider debate about whether literary sequels are a good thing. She said: 'The distortion of works of heritage for commercial ends must be stopped. It's time to defend culture and creativity against the savagery of free enterprise, which seems to want to tarnish everything and reduce every cultural product to the level of the market place.'

But critics Alain Salles and Martine Silber argue in Le Monde: 'Sequels are inseparable from the history of literature. The heirs of Homer would hardly take legal action against James Joyce or his novel Ulysses .'

Good point, but for the fact that Homer's heirs surely aren't aware at this distance in time of their connection to their illustrious ancestor. Anyway, this isn't Joyce, retort Hugo's descendants, it's the literary equivalent of McDonald's. Which is supposed to be an insult.

But several critics doubt that Hugo's descendants are defending a just cause. If the book is lousy, they say, it will fail and not tarnish Hugo's reputation; if it is any good, it can only enrich it.