Michael Redgrave coped with his daughter, Vanessa, by calling her “divinely mad”, and Mark Rylance’s admirers, of whom I’m one, might describe him the same way. He is the finest comic actor of his generation yet also the most earnestly eccentric: a man who has staged plays on England’s ley lines and established Shakespeare’s replica Globe as a leading theatre without believing that the plays he was staging were by Shakespeare.

That scepticism explains the funny-peculiar and (sometimes) funny-ha-ha play that brings him to Chichester as author, lead actor and co-director with Matthew Warchus. His Frank Charlton - is it accident, joke or Freudian slip that the name is close to charlatan? - runs a chat room, complete with visuals, from his tacky Kent garage.

And his obsession is exposing the Stratford pretender, poor old Will Shakespeare.That Charlton is a nerd and loser doesn’t, however, seem to mean that his beliefs are wrong. On the contrary, he’s an excuse for Rylance to bring on stage the ghosts of key claimants to the Bardic bays. After Colin Hurley’s plump Shakespeare has pottered about in red doublet and hose, insisting on his authorship in a Mummerset accent, on come Roddy Maude-Roxby’s bumbling old Bacon, Alex Hassell’s snooty Earl of Oxford and Juliet Rylance’s bubbling Mary Sidney, sister of the great Philip.

The play gets pretty convoluted as their respective cases are put: Bacon that his own words are occasionally echoed in the plays, Oxford that he was a bit of a Hamlet, Sidney that she had the brilliance and empathy to create all those women.

Rylance does his best to enliven the debate, inserting some Stoppardian jokes and introducing an angry copper in the way Shaw irrelevantly introduced burglars when things got dull.

But he’s basically serious and, if I get his drift, suspects that the plays were written by committees of gifted nobs fearful of revealing their identities.

The problem with this is simple. It’s nuts. Yes, Jacobean dramatists often collaborated. Indeed, Shakespeare himself was probably one of six playwrights who wrote Sir Thomas More. But to know his work is to marvel at the evolution of an unmistakably unique voice, mind and soul. And could dry, busy, theatre-hating Bacon find the belief, warmth and energy to write all those plays? And why would Oxford, who died in 1604, have left Macbeth, Lear and his best work in some bottom drawer?

Let’s just remember that his first proponent, back in 1920, was a Mr J. T. Looney.

Surely Maude-Roxby’s Shakespeare is right to say that Charlton, alias Rylance, has “a hang-up about common people creating great works of art”. And if Shakespeare was such an ignorant yokel, why would famous people choose him as a front? Why did his contemporaries, up to sceptical Ben Jonson, believe in him?

At the end of this barmy, likeable play, Rylance asked the audience to cast its authorship votes. For everyone but conspiracy theorists there was one choice: Shakespeare.

— Box office: 01243 781312

Editor's choice

• The 100 Best Films of the Decade
• 70 facts you didn't know about Marvel
• The 50 Biggest Movies Of 2010