A security guard at a London university has been caught on camera in an altercation with students in which they claim he threatened to “kill” one of them – on the same day as the establishment was ranked among the best in the country for freedom of speech.

The guard was filmed by the students as he confronted them while they attempted to put up posters at City University, and a heated exchange follows in which the students claim he told one of them: “Let’s meet outside – I kill you.” The guard then walks off.

According to Scott Campbell, a City student and the editor of an independent publication about the university called The Square, the reporters were threatened, had their campus ID cards confiscated and, he claims, were told their phones would be flushed down the toilet. One of the guards is heard apparently denying they said this.

He told The Huffington Post: “The way security treated us was disgusting, particularly since they are employed to keep students safe.”

The Square has published a number of articles on its website recently detailing the amount of money spent by the University on refurbishing the house of the Vice-Chancellor, which is owned by University, allegedly amounting to £200,000. Campbell said the reporters were approached by security while putting up posters to promote their investigation.

The incident came on the same day as the online magazine Spiked published its Free Speech University Rankings – giving City the highest possible rating.

“City University London and City University Students’ Union collectively create a free and open environment for free speech,” it claimed.

“The university, which has received a Green ranking, holds no restrictions on free speech.”