Comedians invited to perform at a benefit gig at the University of London were asked to sign a "behavioural agreement" that ensured they would only discuss topics in a "respectful and non-abusive way".

Konstantin Kisin, a comedian and free speech campaigner, pulled out of the School of Oriental and African Studies event, telling The Guardian: "I was genuinely shocked. I’ve performed at students unions many times before and never been asked to sign a contract.”

He says he received an e-mail from Fisayo Eniolorunda, who organises the Unicef on Campus society, which read: "Attached is a short behavioural agreement form that we will ask for you to sign on the day to avoid problems."

The message added that the contract had been written "to ensure an environment where joy, love and acceptance are reciprocated by all" and that, by signing it, performers were "agreeing to our no tolerance policy with regards to racism, sexism, classism, ageism, ableism, homophobia, biphobia, transphobia, xenophobia, Islamophobia or anti-religion or anti-atheism.”

It added: “All topics must be presented in a way that is respectful and kind. It does not mean that these topics can not be discussed. But, it must be done in a respectful and non-abusive way.”

Kisin was one of five comedians scheduled to perform at the event next month, which is being held to raise money for Unicef. He said he believes it's vital that comedians are allowed to explore difficult issues on stage unimpeded.

“Obviously performers shouldn’t be allowed to go on stage with the intention of being racist or homophobic,” he said. “But comedians play with ideas and sometimes we stray over the line, or are perceived to have done so. It’s vital that we’re not prevented from playing with ideas in that way or forced to sign contracts that mean if that happens, we’re held up as having broken our word.”

A spokesperson for the National Union of Students said contracts like the one offered were very unusual. They added: "There is little to no evidence that students’ unions are routinely dictating what they can and can’t say,"

“Some students’ unions will have policies to ensure a booking is appropriate; others will not. There is more likely to be a basic ‘sense check’, as would occur in any other venue, to ensure that there isn’t an obvious mismatch between a booking and the audience they’ll be performing in front of.”

Unicef on Campus, which is an independent organisation to Unicef, said in a statement: “We are a group of students who... do not represent Unicef or any student body. We extended an invitation to guests with the idea of hosting a comedy night to raise funds. Given that Unicef is a children’s charity, we wanted to make sure it was an appropriate event for the cause. We would never wish to impose that guests would have to agree to anything they do not believe in. We apologise for the misunderstanding.”

Soas students’ union said it did not require external speakers to sign any form of contract and that the Unicef on Campus society had been "overzealous" in their interpretation of guidelines. A spokesperson said: “The union believes fully in freedom of speech and the freedom to try to make people laugh.”

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