Like the notions that the US faked the Apollo moon missions or that terrorist planes couldn’t have toppled the World Trade Centre, the belief that William Shakespeare didn’t write the plays ascribed to him is one of those enduring conspiracy theories that is very hard to dislodge.

Disaster movie maestro Roland Emmerich is the latest Shakespeare debunker, but his overwrought doublet-and-hose thriller Anonymous will strike most viewers as less credible than Godzilla or The Day After Tomorrow.

Emmerich and his screenwriter, John Orloff, are among those who can’t accept that a mere actor, born the son of a provincial glove maker, wrote the plays we know of as Shakespeare’s. For them, the true author is Edward de Vere, 17th Earl of Oxford, played here by a silky, pensive Rhys Ifans.

As an aristocrat, Oxford can’t put his name to the infra-dig pursuit of writing for the stage so he approaches playwright Ben Jonson (Sebastian Armesto) to act as his mouthpiece.  While the principled Jonson hums and haws, Rafe Spall’s opportunistic Shakespeare, portrayed here as a semi-literate buffoon, hijacks the scheme and claims the Earl’s plays as his own.

The machinations don’t stop there. Ifans’ Oxford is simultaneously up to his neck in the Machiavellian politics of the court of Queen Elizabeth (played as a frisky young woman by Joely Richardson and as an ageing crone by Richardson’s mother, Vanessa Redgrave), matching his wits with cunning statesman William Cecil (David Thewlis) and his hunchbacked son (Edward Hogg) as the struggle rages to secure the succession to the Tudor throne. It’s heady stuff, full of blackmail, backstabbing, cutthroat intrigue and even incest.

Heady, yes. But as history, Anonymous is a complete farrago. The Oxford-is-Shakespeare theory is nonsense (irrespective of the fact that he died in 1604, several years before some of Shakespeare’s best-known plays were written, you only have to read the poetry to which the Earl actually put his name to realise this), and the only way Emmerich and Orloff can make it stick for dramatic purposes is to scrunch and twist real historical events completely out of shape.

But if you can ignore the inaccuracies, jumbled chronology and the often clunky dialogue, Emmerich’s film is a surprisingly entertaining costume romp, ripely acted, vividly realised, and full of all the mud, blood, sex and violence the period can offer.

If, though, you want a fair cinematic account of the creation of Shakespeare’s plays, you’d be far better off with Tom Stoppard’s deliberately fanciful Shakespeare in Love, which is far more plausible and wittier to boot.

On general release from Friday 28th October.