A play starring Hercule Poirot actor David Suchet looks set to be the first in London to be hit by the smoking ban.

Artists in England thought they had won an exemption from the new anti-smoking legislation that comes into effect this weekend, on 1 July.

But Westminster council has warned management of the Theatre Royal Haymarket that it may be at risk of prosecution over The Last Confession play which opens on Monday.

The theatre sought advice after its staff queried the legal position over the Vatican-set thriller about the death of Pope John Paul I in 1978. In one scene, a character called Cardinal Villot, played by Bernard Lloyd, smokes on stage.

Mark Stradling, the theatre manager, was warned by environmental officers the scene might not qualify as necessary for "artistic integrity".

As this could lay the Haymarket open to prosecution, it has told the incoming show that the scene cannot go ahead as rehearsed.

"We can't afford to let the smoking scene go ahead for fear of prosecution. To me it all seems absolutely ridiculous," he said.

"Even in New York, theatres don't have a problem with it. You can't smoke anywhere in New York but it's allowed on Broadway on stage."

The doubts over the scene emerged from a conversation among staff.

"We were all just talking last week and someone mentioned the smoking ban and were we going to have a problem and I immediately said no.

"And then I thought about it and telephoned Westminster council," said Mr Stradling.

An environment officer told him smoking was permissible in some cases, such as "if it was a play about Winston Churchill" who was a famous smoker.

It is understood that Westminster has adopted a position that it will not actively chase theatres over the new legislation,but will act on public complaints. If smoking is not an "artistic requirement," however, plays could be in breach of the law.

Audrey Lewis, the councillor for community protection at Westminster, said they were trying to raise awareness of the legislation.

"Our approach has always been to educate people about it in advance, rather than all this nonsense about 'smoking police' banging on your door," she said.

"But where there are complaints we will of course investigate them in the normal manner, much as we do with issues concerning noise."

The implementation of similar legislation has gone smoothly in other countries, so they expected the legislation to be adopted with a minimum of public fuss, she added.

Actors had previously led a revolt against an all-out smoking ban on stage, winning a concession from ministers to allow it where smoking is "integral to the plot or storyline".

MPs had raised the issue in Parliament saying West End hits such as Who's Afraid Of Virginia Woolf? and The Graduate would be affected if they were staged after 1 July.

Theatres which allow smoking on stage where it was not permitted could be fined £2,500.