The National Youth Theatre (NYT) has been heavily criticised for cancelling a play about the radicalisation of young Muslims.
Leading figures in the arts including the sculptor Anish Kapoo, the playwright Sir David Hare and the actor Simon Callow have signed an open letter calling on the theatre to explain why it pulled the play Homegrown, the Times reports.
The Donmar Warehouse's artistic director Josie Rourke and the Young Vic's artistic director David Lan also put their names to the letter which is published in the Times.
The letter, which was organised by free speech campaign group English PEN, accuses the NYT of failing to defend the play which it commissioned.
The play explored the motives of why someone might be attracted towards extremist groups, such as Islamic State.
Homegrown was cancelled two weeks before today's scheduled opening,when the theatre asked the play's creators whether they were giving a final version of the script to the police.
The director, Nadia Latif, told the Times that one of the play's producers met with police on 22 July 22 who demanded to read the script. She initially refused to send the script to the police, but complied when they asked to see it again a week later.
A week later Homegrown was cancelled.
Neither Latif nor writer Omar El-Khairy do not believe that the police ordered the show to be cancelled, but have accused the theatre of self-censorship because they believe NYT "feared controversy".
NYT standards concern
A statement on the National Theatre website read: "NYT regrets to announce that its production of Homegrown will not now take place… Tickets are no longer on sale. All ticket holders will be fully refunded."
The artistic director of NYT Paul Roseby issued a statement which said that the play, which was to feature 112 young performers and would have been performed in a school building, did not meet the theatre's standards.
However, he declined to meet Latif or El-Khairy to explain the reasons behind the abrupt decision to cancel the play.
The open letter describes the cancellation as "a troubling moment for British theatre and freedom of expression that serves to shut down conversation on these important issues".
"We fear that government policy in response to extremism may be creating a culture of caution in the arts," the letter says, "if it is deemed too risky to ask difficult questions or explore sensitive topics.
"We are deeply concerned by reports that the National Youth Theatre may have been put under external pressure to change the location and then cancel the production."
Latif also accused the theatre of self-censorship and failing to stand up for the play.
"There are lots of ways that we are silenced," she said, "sometimes the most nefarious thing is when artists are silenced by other artists."