Veteran stars Jenny Agutter and Richard Griffiths were forced to climb out of a window to escape a theatre besieged by fans of Harry Potter actor Daniel Radcliffe.

A mob of 450 mostly teenage fans had crowded outside the stage door of the Gielgud Theatre, where 17-year-old Radcliffe is appearing naked every night in Equus.

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Off to see the wizard: Fans crowd around Daniel Radcliffe as he signs autographs outside the Gielgud Theatre, where he is appearing naked every night in Peter Shaffer's Equus

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Police were called to disperse the throng outside the theatre in Rupert Street while Radcliffe's co-stars Griffiths and Agutter were left trapped inside.

Security staff managed to escort Radcliffe to his car, but the two veteran actors ended up having to climb out of a window to avoid the mêlée.

For Griffiths this was a particularly difficult manoeuvre, as producer David Pugh pointed out.

"Richard and Jenny had to get out through the side window by the box office on Rupert Street. You try to get Richard Griffiths out of a back window. It was a bit touch and go," he said.

The previews, including the one attended by police on Saturday night, have already seen a frenzy the likes of which are rare in West End theatres.

But Radcliffe-mania is expected to peak tonight for the press night of Peter Shaffer's play, enjoying its first major revival since its premiere more than 20 years ago. The young star's appearance in Equus has prompted huge interest.

Having played the cleancut boy wizard in a series of multi-million-pound movies since the age of 12, his role as disturbed stable hand Strang was bound to provoke near pandemonium.

In the play, he strips naked for a 10-minute sex scene. He also swears, smokes and blinds several horses.

Mr Pugh estimated half the audience for the previews was made up of people who would not normally attend West End theatres but were coming to see Radcliffe. A large number of cameras have been confiscated before previews.

Equus premiered at the National Theatre in 1973 but Shaffer, now 80, had until now refused to sanction a major revival because he did not believe there was a young actor capable of playing Strang.

Mr Pugh said: "It was only after Peter Shaffer approved Daniel's casting that we thought, 'Ooh, what about the Harry Potter fans?' But touch wood, there has not been a single giggle or whoop or cheer."

During the nude scenes, the audience had remained silent. "You could hear a pin drop," he added.