In most theatres, audiences are reminded to switch off their mobile phones before entering the auditorium.

But in Mark Rylance's ground-breaking new comedy, I Am Shakespeare, theatre-goers are allowed to switch them on - and phone up the actors on stage.

Rylance, the former artistic director of Shakespeare's Globe Theatre, acts as your host in this riotous search for the true identity of William Shakespeare. The Bard's plays are so well written that they have entertained audiences for hundreds of years, but who actually wrote them?

That question is still the subject of feverish debate, and Rylance has removed the whodunnit from the dusty halls of academia and given it a distinctly modern setting.

Teacher Frank Charlton, played by Rylance, is so obsessed with the authorship question that he sets up an Internet chatroom entitled I Am Shakespeare.

During a lightning storm, he finds himself confronted with the real William Shakespeare, the real Francis Bacon, then Edward de Vere, Earl of Oxford, and finally the real Mary Sidney.

Frank then interviews each of the four characters to see who has the strongest claim to be the real author.

One of the highlights of the show involves members of the audience when they are asked to use their mobiles to phone the chat room show.

Sean Foley, who plays Frank's ex-pop star neighbour, said the play got off to a great start in Chichester, with some famous names phoning in: "Dame Joan Plowright, who is Baroness Olivier, called up and asked why we can't dig up Shakespeare's bones so that they can be carbon-dated. Then we had a call from Derek Jacobi, so who knows who we will get in Oxford?

"When the calls come in everyone on stage improvises. There are periods where there is an answering machine on, but most of the time the chat-room show lines are open."

Foley, a co-founder of the double act The Right Size, said the comedy was the nearest he had ever got to playing Shakespeare.

He added: "It's very innovative but I don't think it's difficult to categorise - it's a funny show about who wrote Shakespeare."

I Am Shakespeare is co-directed by Lord of the Rings art director Matthew Warchus, and designed by Jenny Tiramani, an international expert in Elizabethan and Jacobean clothing, and winner of the Laurence Olivier Award for Costume Design in 2003. It is produced by London Theatre of Imagination and Chichester Festival Theatre and presented on tour by Greg Ripley Duggan.

Performances run from Monday to Saturday. Call the box office on 01865 305305.