ben sullivan
Ben Sullivan was elected Oxford Union president unopposedYouTube/Oxford Union

A series of high-profile keynote speakers have cancelled their appearances at the world famous Oxford union debating society following the return of its president from police questioning over rape allegations.

Interpol's security general Ronal Noble is the latest speaker to pull out of a talk at Oxford University over concerns about the union's president Ben Sullivan.

"What should the head of a society like the Oxford Union do if he is under investigation for rape and attempted rape?" said Noble. "In my view, he should be guided by the best interests of his organisation. He should not be guided by his own interests.

"In this case my advice to Ben Sullivan would be either to resign or take a leave of absence until the criminal investigation has been completed."

Noble joins a list which includes UK director of Human Rights Watch David Mepham and BBC Dragon's Den judge Julie Meyer to have postponed or pulled out of their scheduled appearances since Sullivan was questioned on 7 May.

Sullivan, 21, was arrested by Thames Valley Police on suspicion of the rape and attempted rape of two undergraduates at the prestigious university.

After being released on bail, until June 18, he went back to his post as chair of the debating society.

However his return to duty angered some students and prompted an open letter penned by Sarah Pine, Oxford union's vice president for Women, and Helena Dollimor, a second year history and politics student at St Hilda's College, calling for Sullivan to stand down while the investigation is ongoing.

The letter states: "Remaining in his presidency continues to offer prestige and power to someone who is being investigated for rape. This undermines the severe nature of allegations of sexual offences.

"We note that Mr Sullivan has previously attempted to use union funds to finance his legal actions against the press. This is a misuse of his office and makes a mockery of the society's core principle of freedom of speech. This record leads us to lack confidence in his future presidential conduct while under investigation for sexual offences.

"The anger with which Oxford students have reacted, combined with speakers cancelling their appearances due to the controversy over his continued presence, means he should not remain in office."

Mepham added: "I believe people are innocent until proven guilty, but I've decided to postpone my speech because they obviously have a lot going on over there."

Journalists Owen Jones and Laurie Penny and feminist activist Caroline Criado Perez are among those who have signed the letter to the university.

Noble said Interpol tried to contact Oxford Union since Sullivan was arrested but had not received a response.

Former prime ministers William Gladstone, Herbert Asquith and Edward Heath are among those who have previously held the post of president of Oxford Union.