The National Theatre is staging a “provocative” play about paedophilia aimed at showing perpetrators "some measure of understanding", as its writer suggests sexual abuse is not “black and white”.

The play called Downstate, which had police protection at the theatre when it opened in America over fears of protests, is about “forgiveness”, said writer Bruce Norris.

Described by the National Theatre as “provocative” and based in Illinois, it tells the story of four men convicted of sex crimes against minors, who share a group home where they “live out their lives in the shadow of the offences they committed”.

The National Theatre, which includes links to child abuse and mental health charities on the play’s section of its website, warns those considering buying tickets: “Downstate discusses and contains graphic descriptions of child abuse and rape.

“There are also graphic depictions of self-harm and reference to drug use, that some people may find distressing.”

At a Q&A at the theatre on Friday, writer Bruce Norris and director Pam MacKinnon explained the purpose of the play: to “disrupt consensus” and question whether what is currently considered sexually appropriate today will seem “somewhat barbaric” in 100 years.

“The idea that these sort of legal and sexual situations were being treated as black and white makes me really uncomfortable, because that is a form of consensus that I think is not nuanced enough to address what actually goes on in those situations,” said Norris.