Tsui served two five-year terms after almost 30 months as the university's interim leader. Professor Peter Mathieson, the former dean of medicine and dentistry at the University of Bristol in Britain, will succeed Tsui as the university's 15th vice chancellor. Tsui has not said what he plans to do in the future.

Tsui's last months have been marked by tension, with some faculty members expressing concern that politics could be undermining academic freedom. In an interview with the , Tsui reflected on his 12 years at HKU. He said it was important for the university to learn from society.

"There are things we can learn from the society, such as social work and education," he says. "How would we know it if we don't work with it?"

Tsui played down concerns that faculty members had been active in politics, particularly the city's pro-democracy movement. Benny Tai Yiu-ting, an associate law professor at HKU, is a leader of the movement known as Occupy Central, which is pushing for full voting rights for adults in the 2017 chief executive election.

Tsui says he believes it is important to respect different voices on campus, adding that it is the essence of academic freedom and key to the university's DNA.

"I will not interfere with individual staff members, and I trust my colleagues, such as Professor Johannes Chan {Man-mun], the dean of law, who would not impose his political beliefs on the administration, but instead would ensure space and openness for different opinions," Tsui says. "That I think is very important for a university."

The vice chancellor is also adamant about the need for HKU to remain an international institution. "One should not forget our university was international right from the start, simply because there weren't enough local people to fill the roster," he says. "Our recruitment should be based on qualification and needs, and not nationality."

The university has used quotas to admit many more mainland students in recent years, prompting complaints by some Hong Kong residents.

Of the nearly 71,000 undergraduate applications received in 2012, more than 23,800 came from students outside the Hong Kong schools system, according to the university. One in nine applicants received an offer of admission. More than 6,800 of the 10,795 students who enrolled in the 2012-2013 school year required a visa.

"We have an agreement that non-local students can exceed no more than 20 per cent of all undergraduates," Tsui says. "But only 4 four per cent of these non-local students receive a government subsidy, taxpayers' money, and 16 per cent are privately funded. Besides, only half of the 20 per cent are mainland students; the other 10 per cent are students from all over the world."

Tsui says there is much to be gained from students coming from outside of Hong Kong. Local students may just experience "an extension of the secondary school experience", he says. "But with more classmates from different cultures and backgrounds, discussion shoots up, the entire classroom dynamic changes. Projects, using fresh perspectives or methodology, bring about results that are especially encouraging to the teaching staff."

"The same can be said of post-graduate students" - whose numbers are not set by quotas - he says. "It's a basic academic concept to get and nurture the best young scholars and bring them in to boost our research. If non-local students choose HKU out of their appreciation of our teaching standards and facilities, I think we should give ourselves a round of applause and be proud of it."

As for teaching staff, Tsui says the policy has moved on from recruiting renowned professors to young scholars.

"Famous scholars are effective in building up a curriculum, but not so conducive to long-term sustainable development and they could make it difficult for young scholars to advance in the faculty," he says. "So we have now with us a group of young scholars with proven potential."

Tsui's tenure was engulfed in controversy in August 2011 when Li Keqiang , then a Chinese vice-premier, visited HKU. Police, according to a subsequent report, locked down parts of the campus and used "unreasonable" force when officers confined protesters to a stairwell and pushed a few students. Tsui was accused of pandering to the central government and using "bad judgment". Tsui subsequently apologised to the university community. Two months later, Tsui announced his resignation.

Tsui laughs when asked if his resignation was linked to the incident.

He then turns more serious and says that before Li's visit he had asked that his appointment be renewed for just three years after the second term expired in 2012. He says that the university council's chairman, Dr Leong Che-hung, had asked him to serve a full five-year term.

"The timing [of the incident] was unfortunate," Tsui says.

Tsui adds that what upset him most was that "a few students did not see the picture clearly and just jumped on the bandwagon and charged", he says. "Has academic freedom been affected in any way since? I must say that that is the university's cornerstone, and will forever be so."

Tsui notes the memorials on campus that commemorate the 1989 Tiananmen crackdown, including the , part of a sculpture series by Danish artist Jens Galschiot, as well as the two protest slogans painted on the pavement of Swire Bridge.

"Those relics are a part of HKU culture," he says. "Many mainland students have never heard of June 4. Young local students did not witness it. So there's a lot of hearsay about the incident. These things will offer some history for them to learn.

"Previously some were concerned that state leaders visiting the campus should be kept away from these things. It's really unnecessary as we all know what happened."

Tsui has served the university during times of great change: from the Sars epidemic, to the completion of major projects including the new Centennial campus, and the forthcoming opening of an MTR station. Tsui says, most of all, he will pine for the people of the university.

"It's the HKU family, and the supportive alumni and the community at large, that I am most proud of and will miss," he says.

Tsui says he is not interested in joining the government, even in the new Innovation and Technology bureau that Chief Executive Leung Chun-ying mentioned in his last policy address.

"I like innovation and research, but implementing it is something else. In that I am not so interested, at least for now," he says.

A biologist, Tsui once worked at the Oak Ridge National Laboratory, a US government lab in the state of Tennessee. He also held several positions in Toronto, including the HE Sellers Chair in Cystic Fibrosis at the University of Toronto. In 1989, Tsui was part of the team that discovered the cystic fibrosis transmembrane conductance regulator gene that causes the glandular disease.

Tsui says that it is unlikely that he will return to genetic research on chromosomes.

"Want to know how much the world has changed in the past 12 years?" he says to the question. "Compare your mobile phone now to the one you had then."