University College London has apologised to current and former students and staff for a “culture of unacceptable behaviour” at its architecture school going back decades.

The apology comes after the university conducted an investigation into complaints of sexism and racism on campus, first reported by the Guardian last year.

“I want to apologise to everyone who has suffered because of the culture of bullying, harassment and sexual misconduct within the Bartlett School of Architecture,” said Michael Spence, UCL’s president and provost, in response to the internal investigation’s findings.

The inquiry, which began in October 2021, concluded in mid-April with findings detailed in an 119-page report by Howlett Brown, an intelligence company specialising in employee investigations and appointed by the university as an impartial investigator.

In the report, Howlett Brown said it learned some “uncomfortable truths and several ‘open secrets’ about the BSA”, citing power, protectionism, a “boys’ club” culture that allowed a lack of accountability, and a fear of speaking out “woven into the fabric of the BSA for a long period of time”.

The investigation included 49 individual interviews, focus groups, written submissions and a survey with more than 300 respondents.

A dossier shared with the Guardian in 2021, and cited in the final report, included testimonials from 21 people claiming there were “systemic” problems at the Bartlett. The testimonials, compiled by a student who experienced sexism while studying at the institution in 2000, alleged inappropriate comments were made about appearance and race, and said female students were sometimes brought to tears.

“Their testimonies expose an inexcusable and pernicious underbelly of bullying and other unacceptable behaviour that is completely at odds with the values on which UCL was founded,” said Spence. “We must, and absolutely will, address that swiftly and robustly.”

The report said serious allegations “spanning the last three decades” involved a number of staff allegedly making sexist comments and verbally attacking female students, in addition to allegedly misogynistic, discriminatory, and antisemitic behaviour.

One participant said they were told by a tutor “you should be grateful for what your family has immigrated to”. Another former student said “the environment was very toxic, especially for women, working-class people and individuals of colour”. A student who said she was raped by a fellow student did not share it with members of staff as she wasn’t sure “there was a network in place”.

Other staff members were alleged to have inappropriately touched students, partied with students while taking drugs, and dated students during their time at the school.

The report, which said the problems began to appear in the early 1990s, also cited a “varying degree of complacency” among other staff members, described as complicit through their inaction, and exacerbated by a lack of oversight, accountability or action.

The report urged the university to investigate allegations about BSA staff further, recommended a shift in the structure of hiring tutors, in staff training, and offering long-term counselling and support options.

Citing an “inherent power imbalance”, the report said the university’s personal relationship policy, which has a blanket ban on relationships with those under 18, fails to safeguard students from sexual harassment and inappropriate conduct.

Christoph Lindner, the dean of the Bartlett Faculty of the Built Environment, which is home to the Bartlett School, said: “This report contains shocking testimonies and highlights a number of unforgivable incidents.”

After the report came out, a number of staff from the architecture school were removed from student-facing and administrative duties with “immediate effect”, according to the university, while further investigations were carried out.

Lindner said: “It’s time for us to have some difficult conversations about how we disrupt existing structures of privilege and power, making space and opportunities for those who have previously been marginalised.”