In a red-brick house in the Hampshire village of Chawton, Jane Austen sat down to write to her sister Cassandra.

"I want to tell you that I have got my own darling Child from London," she said. This "child" was her second novel, Pride & Prejudice, and while she was clearly thrilled with it, she adopted a typically satirical tone: "The work is rather too light, and bright, and sparkling; it wants shade; it wants to be stretched out here and there with a long chapter of sense, if it could be had..."

Surely, the most influential novel ever written, Pride & Prejudice was published anonymously on January 28, 1813, in three calfskin volumes, at a cost of 18 shillings. About 700 copies were printed. To mark its two hundredth anniversary, an antiquarian bookseller is offering a rare first edition for £65,000. I doubt I'm only one who looked covetously, and rather too long, before closing his email.

By the 1820s, when Pride & Prejudice languished out of print and favour, it would have been inconceivable to think that in 2007, British readers would vote it the book "the nation can't do without". Following Austen's growing commercial readership and academic acclaim since the Second World War, her novel has not only shaped the rules of realistic romantic fiction, but spawned countless imitators, spoofs, prequels, sequels, TV series and films. In fact, if anyone should snap up that pricey first edition it should be Colin Firth, who owes much of his success to his sensual depiction of brooding Mr Darcy, thereby sealing that character's fate as literature's favourite hero.

Yet despite lush, sentimental screen adaptations which turn Austen's pin-sharp portraits into a nostalgic wallow, the novel is assiduously unglamorous. Nor does it present a world any of us would really want to live in. Though spirited and witty, it is very much of its time. Putting aside the literary genius and Austen's astonishingly original style, Pride & Prejudice remains a narrowly focused work about a society of middle-class and aristocratic busybodies and idlers. What can such a book possibly have to say to a supposedly egalitarian age such as ours, and why is it still so popular?

Some would suggest it is Austen's characters that amuse us, her eccentrics and egotists as recognisable today as they were to her. But many novelists have created unforgettably vivid characters, and since human nature has not changed since Cleopatra's day, their familiarity hardly explains the timeless appeal of Austen's cast. Rather, it is her humour that endears the story to us, comedy now being the surest way to our hearts. That, and of course, a directness of voice, and economy of style, that chime with today's readers more than they ever would with Victorians.

In Pride & Prejudice Austen gives the illusion of catching life and its players exactly as they were: young Lydia, the lustful airhead, Charles Bingley, weak but sweet, and Mr Bennet, a sardonic father who is loving, lazy and a little callous. With these, and all the others, Austen so cleverly draws us in we feel we are watching events through a window, and forget we are in the hands of an arch-manipulator whose supreme talent for drama, and dialogue in particular, hides the artifice behind every line.

But there's something even more important. One of the reasons we never tire of Austen, I believe, is because in many ways she was ahead of her time. Her irreverent eye, her love of poking fun at the pompous, and her ambivalence towards her far from perfect heroines and heroes, strike a distinctly modern note. Previous generations might have frowned at her lack of piety, and her obsession with money and status, as when Elizabeth finally falls for Darcy, just as she's being shown around his extensive parklands. But this was Austen being scrupulously honest. Life for characters in Pride & Prejudice is not rose-tinted. If Mrs Bennet could not find husbands for all five daughters, lean times lay ahead. If plain spinster Charlotte Lucas had not married insufferable Mr Collins, her future was bleak. In fact, the only thing that rescued Austen from a similarly anxious fate was her pen. Rarely has ink been spilled to better purpose.