Derek Jacobi rushes into a contemporary New York theatre to give a talk about the authorship of Shakespeare's plays. In real life, Sir Derek thinks the Earl of Oxford wrote them. And that's his story on the stage, too, melding as a prologue into the controversial new film Anonymous.

Jacobi appears alongside another non-believer, Mark Rylance, who plays the actor Henry Condell (who co-published Shakespeare's First Folio) delivering -- not very well, as it happens -- famous speeches of Henry V and Richard III in a CGI reconstruction of the Globe.

Roland Emmerich's film also features Vanessa Redgrave as a bonkers old Virgin Queen -- well, actually, not so Virgin, as in this story she is both mother and lover of Oxford, with whom she conceives the Earl of Southampton. The narrative is a terrible muddle of flashbacks and non-chronological inserts, not helped by the fact that the young Elizabeth is played by Vanessa's daughter, Joely Richardson.

Shakespeare himself is represented by Rafe Spall as an illiterate, alcoholic buffoon, his name used by Oxford as a cover for his writing career; noblemen were not supposed to muddy their hands with the theatre, though if there's one single salient feature of Shakespeare's plays it is that they reek of stagecraft and the experience of, and deep interest in, performing.

The go-between is the unlikely figure of Ben Jonson, and the whole farrago -- I may as well use the word as almost everyone else has -- is wrapped up in a ludicrous account of the Essex plot to overthrow Elizabeth.

The barmy assertions of the film would matter less -- in fact, they wouldn't matter at all -- if the script was half way decent, or the acting. But they're not. Rhys Ifans as Oxford is as animated as a waxwork; Spall junior is reduced to muttering unfunny, anachronistic asides when his lines run out; and Tristan Gravelle as Christopher Marlowe (in whose death Shakespeare is spuriously implicated) comes across as the Nick Clegg of Bankside.

The chairman of the RSC, Jonathan Bate, thinks the film looks beautiful. But it also looks like any routine re-design of Elizabethan London, with a Toy Town proximity between the Globe and Whitehall,  and the obviousness of the CGI effect becomes deeply depressing after a while. The entire action seems to have been shot at four in the morning, in a cold and grey Scandinavian landscape and climate.

The fact that the Earl of Oxford died in 1604, before eight of Shakespeare's greatest plays were either written or performed, is semi-explained by there being a stash of stuff that Oxford entrusts to Jonson for future reference on his death bed.

But as Philip French said in the Observer at the weekend, the most cursory glance at James Shapiro's magnificent book about the authorship controversy, Contested Will, would have taken the wind out of Roland Emmerich's sails.

For the silliest thing of all is that the film is being distributed in America with an educational package that asserts that Shakespeare went to a village school that could never have provided him with a vocabulary extensive enough to write his own plays.

This argument was summarily dealt with in Simon Callow's solo Shakespeare show, scripted by Bate, in which the curriculum of Stratford Grammar School was itemised in all its richness and glory; that education was far more "extensive," Bate says, than anything that might have come the way of a privileged courtier like the Earl of Oxford.

Professor Stanley Wells is fuming about the film, but as Bate revealed in Bryan Appleyard's excellent Sunday Times feature, the idiocy of Anonymous is somehow both understandable and a tribute to the Bard: "The capaciousness of his imagination, combined with the reticence of his work in not actually revealing him, forms a gap in which everybody can project their own fantasies onto Shakespeare."

Every time someone writes Shakespeare the character, elements of envy and revenge are involved. Edward Bond's view of Shakespeare in Bingo, numbed into inertia by the failure of his theatre writing to have had any effect on the way he lived, is far more interesting, and it's good that Patrick Stewart will be repeating that performance next year in London, the third time he has played the role. 

You could call it the "Amadeus" effect, in which the comparatively mediocre composer Salieri is unable to understand, or tolerate, the unfairness of Mozart's genius. But thanks to scholars like Bate, Wells and Shapiro, we don't, in Shakespeare's case, have to resort to the God-speaking-through-Mozart line of argument.

The evidence for his authorship is apparent in everything he wrote; and it's both sad and beautiful that none of us, not even Hollywood film-makers or Derek Jacobi, can truly call him to account.