It is a truth universally acknowledged that an author in possession of a book contract will borrow heavily from Jane Austen. Although Bridget Jones was based on Pride and Prejudice, the fiercely independent Lizzie Bennet does not require a Knight In Shining Armani to make her happy. She is much more radical than insipid Bridget Jones types - women who've kept their Wonderbras and burned their brains. Bridget feels she's a romance fatality: this diary-writing doppelganger is so desperate to lose her "singleton" status that she's husband-hunting with everything but a net and a tranquilliser gun. Lizzie Bennet, however, will marry only for love.

It takes a while, when reading Austen, to realise how subversive she really is. The prose is so beguiling, the sentences so beautifully crafted, that it is only after a few chapters that you feel the need to fasten your psychological seat belt for a wickedly bumpy ride. Austen's work is a barbed commentary on the battle between the sexes. She knew, as a woman, that poetic justice was the only justice in the world - and set about impaling misogynistic enemies on the end of her pen. She was scathing of a society in which women were merely domestic or decorative. With no vote, no trade union, no fixed wage, no welfare and no contraception, the only options available to the female of the species were governessing, domestic service, prostitution or marriage (often a tautology, in those days). Wedlock was little more than a padlock, with wives compelled to pledge obedience. "Insanity" and "moral unfitness" were grounds for men to divorce their wives, depriving them of their children and casting them forth from the marriage bed to Bedlam.

But does Working Title's latest project reflect Austen's proto-feminist agenda? Joe Wright's film is effervescent, invigorating and visually ravishing. The director captures the chaos and camaraderie, the bonhomie and banter of a house full of sisters. (I have nearly as many as Lizzie.) Girlish giggles fizz to the surface like champagne bubbles.

The accomplished acting charms and disarms. The ill-matched parental bookends are played by Donald Sutherland and Brenda Blethyn, Judi Dench is the imperious Lady Catherine de Bourg and Tom Hollander is the excruciatingly amusing social climber Mr Collins, a cleric who has ascended to such heights that he's getting nosebleeds. Matthew MacFadyen, however, has bigger breeches to fill, following hot on the riding-booted heels of Colin Firth's Mr Darcy in the much-loved BBC television version. MacFadyen broods about the place like a rain cloud on a sunny day. But although not quite handsome enough to hijack a woman's hormones immediately, his nervous, passionate declarations of love are convincingly endearing. When the star-crossed lovers do almost kiss in the rain, the screen sizzles with heat - so much so, I feared it would trigger the cinema's automatic sprinkler system.

Keira Knightley is enchanting, but far too beautiful for the part of Lizzie Bennet. Lizzie is witty, not pretty. The joy of the novel is that Lizzie's chronic scepticism and wry witticisms, not her looks, win her the tall, dark and bankable one. Knightley, however, has the kind of face you associate with the speech "I'd like to travel the world and meet interesting people". It is totally implausible that this exquisite countenance would prompt Darcy to mutter to Bingley (the delicious Simon Woods) that Lizzie is "tolerable, but not handsome enough to tempt me". What is he - gay? Lizzie's sister Jane (delicately and delightfully played by Rosamund Pike) is supposed to eclipse all with her celestial beauty. Next to the chocolate-eyed Keira, however, she is a very plain Jane: a bland blonde.

The film fails to convey the desperation and claustrophobia of women's lives in the Regency period. This was an era when females were sold, like cattle, for breeding purposes, to the highest bidder. The film addresses this issue only momentarily, when Lizzie's best friend, Charlotte (the excellent Claudie Blakley), accepts the marriage proposal of the odious, oleaginous Mr Collins. With her shelf-life about to expire, and knowing she's a burden on her parents, Charlotte has no option but to knot her nuptials. This frantic search for a member of the ring-buying sex forced women to downgrade their marriage prospects from Mr Right to Mr Vaguely Bearable.

Wright has said that his aim was to "take a new approach to Pride and Prejudice". As we now know that marriage suits men much more than it suits women (married men live longer than single women and suffer less from heart disease and mental problems, whereas single women live longer than married women and suffer less from heart disease and mental problems), a truly updated version of Pride and Prejudice would have a harried Mr Bennet trying to marry off his five burdensome sons, while the female characters remained footloose and fiance-free. Now that would be new.