Pupils on a school trip to the theatre were ordered to leave a play when their teachers were shocked by a sex scene.

As the first act of Entertaining Mr Sloane, directed by film star Patrick Bergin, ended, the teenagers were shepherded from their seats.

Other audience members at the matinee waited as Mr Bergin attempted to persuade teachers to allow the 57 pupils from Dorothy Stringer High School to stay, promising to tone down the performance in the second half.

But even the Sleeping With The Enemy star's Hollywood charm failed to convince them.

The play was eventually cancelled and other theatregoers given free tickets to a future performance at the Old Market Theatre in Hove.

Mr Bergin said: "I wouldn't have minded so much if the pupils had been bored but they were enjoying the show."

The BrightonHove Theatre Company has agreed to give the school in Loder Road, Brighton, a full refund.

The offending scene, at the end of the first act of the 1964 Joe Orton play, features middle-aged landlady Kath, played by Kyla Moore, in a flimsy negligee sitting astride her young tenant crying: "Oh, Mr Sloane!"

Mr Bergin said last night he had deliberately asked the cast to tone down the raunchier scenes because of the presence of the school party. He said he had arranged for the lights to be dimmed earlier and had told Miss Moore and Pieter Vodden, who plays the eponymous lead, not to overdo it.

He had also cut another sex scene which opens the second act.

Mr Bergin said: "It's very disappointing. People know this is a risqu play.

"There's no nudity. The actress had her nightie on and Mr Sloane is fully clothed. There is nothing in the scene that you don't see on TV.

"We deliberately calmed the scenes down and there was only one cry of, 'Oh Mr Sloane' instead of the several in the evening performances.

"Because of the length of time the discussions took and the atmosphere created we decided to cancel the performance altogether and give tickets to the rest of the audience for them to come back and see the play before it ends on Saturday night."

A theatre spokesman said: "It was disappointing they had to leave but they should have known the kind of play it was. After all, it has been around for nearly 40 years."

The play, first performed in 1964, is regarded as a Sixties classic. It has been made into a film and studied by drama and English literature students for GCSE and A-level.

The school's headteacher, Trevor Allen, said the pupils were theatre studies students who attended live performances as part of their coursework.

Staff checked with the director beforehand as to whether the play would be suitable and were told it would be.

They were assured there would be no swearing, no nudity and that the lights would be cut - or blacked out - when the simulated sex scene took place.

The lights were not cut and the teachers decided the play was not suitable.

Mr Allen said he fully supported the teachers' decision to leave the performance.

"I would have been critical if they had not done that," he said. "A judgement had to be made and I support that judgement."

He also said the play's advance publicity material didn't give a warning as to its nature and he wondered whether the pupils were being used as a promotional stunt to sell more tickets.

He also couldn't understand why the performance was cancelled after the school party left since there were other members of the audience.