In New York last weekend, a huddle of typically hard-boiled American film critics gathered for a private screening of a new release, Shakespeare in Love.

By the time our bunch of jaded viewers left the screening room, they were convinced they had seen a masterpiece, the most finely written and acted romantic comedy of the year: an Oscar cert. The title is self-explanatory: the promising young playwright William Shakespeare - played by Joseph Fiennes - falls in love, curing himself of a bad case of writer's block in doing so. But out of this simple idea Tom Stoppard has spun a predictably witty and ingenious screenplay, and what you get alongside a dramatic love story is a sparkling drama that cheekily writes its own version of how the Bard came to write his plays.

Stoppard's Shakespeare is not just a historically accurate-looking man in doublet and hose. He has filthy inky fingers, untidy clothes and an eccentric approach to his work. Before sitting at his desk, he rubs a fresh quill between his fingers, turns on his heel with a flourish and spits in the corner. ("This was in the script," says Fiennes. "I assume Stoppard has some kind of ritual himself - nobody questioned it.") We see not a man in a reverie of creativity, but a real playwright, jostling with his actors and fending off pirates of his work, and a real man, passionately bedding his beloved Viola.

But while preparing a comedy, which Stoppard gloriously gives the working title Romeo and Ethel - The Pirate's Daughter, he suffers from writer's block. He falls in love at first sight with one of his fans, Viola De Lesseps (Paltrow), who, like all women of the day, was not allowed to act on stage. So driven is she by her love for Shakespeare's work, she disguises herself as a moustachioed boy, Thomas Kent, to win a role in Romeo and Ethel, which is being written and rehearsed at the same time. Soon Shakespeare is confiding in Thomas Kent, confessing to "him" his love for the high-bred Viola . . . and acting out in person the duplicity that will become the basis for his later comedy Twelfth Night.

Stoppard spins the idea still further: as Shakespeare writes more of Romeo and Ethel, with words suddenly released like a torrent since he fell in love with Viola, he begins to shape it as a tragedy not so far removed from another, more familiar Romeo play. It mirrors the insurmountable problems of their own affair: he has a wife and children at home in Stratford-upon-Avon, while Viola has been betrothed by her father, Sir Robert (Nicholas Le Prevost), to the insufferable Lord Wessex (Colin Firth).

The script weaves between authenticity and pure invention, between comedy, tragedy and pathos. At its heart is the supposition that Shakespeare was, in reality, a highly talented but flawed man who wanted to make a good living from his work.

Henslowe, who as a matter of historical record also ran a brothel and a bear pit, is projected as a 16th-century Arthur Daley, ducking and diving from his debts while striving to land a hit play that would pay his backers, debtors, actors and family. As the film's director, John Madden, notes: "We have ended up with one foot in the 16th century and one in the 20th, which is perfect."

Some scenes, as Firth observes, "could easily have slipped into Carry On Shakespeare, because of the slapstick"; there are others, in which Paltrow finally abandons her pledge never to appear in a naked love scene, that are racy and sexually charged.

There are twists and surprises: Queen Elizabeth (Judi Dench), sans teeth, her white face-mask cruelly cracked; the playwright Christopher Marlowe (Rupert Everett), stabbed to death at the age of 29 in a tavern-house brawl, advising Shakespeare how to approach his writing; John Webster, an early 17th-century horror writer (The White Devil; The Duchess of Malfi), being introduced as a boy who likes torturing mice.

Rush [right] comments: "The script had 'Eat Me' on the front page. I was soon belly-laughing when one Elizabethan says to another, 'Talk prose.' But there was a little voice in the back of my mind, thinking: how is Stoppard going to maintain this level of wit, particularly with a plot that is going in very peculiar directions? Once I started doing research on the real Henslowe - his diaries are available to be read by the public at Dulwich College - I realised that this part was written so well, because he was a commercial shark. He wanted commercial crap to fill his theatre - not art."

The niggling doubts did not finally subside for the perfectionist Rush, though, until last weekend's screening, when he saw the film for the first time. "Once I started working, I was enjoying myself so much that I thought: is this going to be a great shoot and a lousy pic? But I watched the film with a friend who almost fell off his seat when Wessex grabs Shakespeare and says, 'I am going to spill your blood, but not now. What is your name?' And he says, 'Christopher Marlowe.' "

One of the main drawbacks in trying to portray William Shakespeare as a screen character - although Stoppard turns it into an advantage - is that so little is known of his life. "We don't know much more than that he paid £50 to join the Chamberlain's Men as an actor and that in his will he left his second-best bed to his wife," says Madden. "We all have a theory. Mine is that he was just a jobbing actor and writer with a knack, a true gift. But no doubt he had money troubles and suffered from all the rivalries of the theatre world he lived in."

Madden was not the first choice of director for this film. When the film was bought up 18 months ago by Miramax, Madden, by his own reckoning, was in the right place at the right time. Miramax's Harvey Weinstein was impressed by Madden's previous film, Mrs Brown, and handed him the Stoppard script. "By the time I had finished page one, I knew I'd never be offered another one as good," Madden says. "What it meant to me was that I would be able to get virtually every actor I wanted, just by showing them the script. Even the tiniest role has an interesting journey, and everyone has something to say."

Which explains why every role in the film has a star name attached. Paltrow abandoned her idea of taking a break from back-to-back filming to do it; Dench told Madden she would take any part, "even someone slouching in a doorway".

Actors of the calibre of Tom Wilkinson, Simon Callow, Imelda Staunton, Jim Carter and Antony Sher put in appearances, as does the American Ben Affleck, appropriately cast as Ned Alleyn, the star actor of the day.

For his Shakespeare, Madden trawled a range of star actors, before settling for Fiennes - currently appearing in another tights-role as Lord Dudley in the acclaimed film Elizabeth. "He needed to have intense romanticism, a gift for comedy and a mysterious personality," the director reasons. "An audience needs to believe he could have actually written the plays."

Fiennes, who worked for the Royal Shakespeare Company in Stratford-upon-Avon for two years, feels strongly that it is a pity the Bard has been turned into such an icon. "This film brings out all the human elements, the sentiments and problems that go with being a man of his profession at that time - all the things that nobody associates with genius. To a certain extent, I had to put aside my own reverence about the writer of such great works and just get on with it. I had to adopt the attitude that as soon as I put on these tights, I am Will Shakespeare. "On issues of religion, sex and politics, he will always be a mystery. So I had to think: he is a young guy called Will, looking to make a packet, get his name in lights, secure the rent and make sure his family is looked after. He was my age when he wrote Romeo and Juliet, so I have a feeling for his emotions at the time. I think he was a sinister romantic. There is absolutely no evidence to point towards such an affair with a woman already betrothed, but I have a feeling that it's probably as close to the truth as we will get." Read the full article here.