Professor Tim Luckhurst, who heads Durham University’s South College, made the remark when the students walked out during the controversial speech by right-wing journalist Rod Liddle on Friday. He also reportedly shouted “at South College, we value freedom of speech!”

Liddle, who works for The Spectator magazine, had accused the political left of ignoring science when it came to transgender issues. According to The Telegraph, he also argued colonialism is “not remotely the major cause of Africa’s problems” and claimed that institutional racism was not to blame for underachieving black students. Students apparently shouted “disgusting!” and “racist!” at Liddle as he left the venue later.

Although Luckhurst emailed students to apologize, the university launched an investigation into his conduct over the weekend, as a “matter of urgency.” While “categorically” disagreeing with Liddle’s comments, school authorities noted that they were “concerned” about the “behaviours exhibited” during the evening, which fell “short of those that we expect.”

Luckhurst has reportedly been barred from official duties and placed under a gag order regarding the controversy. The university’s student union has reportedly stated his position at the institution was “untenable” while the University and College Union, which represents lecturers, said it was “utterly appalled.”

After the speech, a poster by LGBTQ charity Stonewall that read “Some people are trans. Get over it!” was apparently pasted on the door of Luckhurst’s office. According to student newspaper Palatinate, a number of students are organizing protests against Luckhurst this week.

In addition, students have written an open letter to the university’s vice-chancellor, criticizing both Liddle’s remarks as “transphobic, sexist, racist and classist,” as well as the decision to invite him to the event. The letter, signed by more than 1,000 people, calls for Luckhurst to apologize. Student groups have also demanded greater transparency in the selection of guest speakers at college events.

Following the backlash, Luckhurst apologized to students via an email that reportedly said the students had “as much right to absent themselves from the speech as my guest had to make it.” He said his outburst at the walkout “reflected my sincere commitment to freedom of speech.”