A couple of weeks ago, a troubled member of staff came to see me for a confidential meeting. He had started a relationship with an undergraduate and thought he'd better confess.

"She's a third year," he blurted, hoping this might mitigate the offence.

"Oh well, that certainly helps," I mused encouragingly, wondering where I'd filed the number of the university lawyer. "And is she on your course?"

She wasn't. She wasn't even in his department. I breathed a sigh of relief. That was something. At least he wasn't teaching her, or even worse, marking her coursework, leaving him open to blackmail and making the university potentially guilty of unsound academic procedure.

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We went on to discuss the other possible ramifications of his entanglement: his terror of being compromised; his concern about whether the student's reputation might be damaged; his sheepishness about the age gap; and, not least, what might happen if they split up. Wouldn't it be best, I suggested, to cool things until after finals?

What struck me about the episode was how different it was from my student days. In the 1960s, affairs between students and lecturers were so commonplace that no one even recognised there may be problems, although some tutors did take the new freedoms a bit too far. One professor was so notoriously promiscuous, a story went around that whenever he left the house, his neighbours would rush out to bring in their cats.

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But this was a time when sexual freedom was not just condoned: it was celebrated as part of the new radicalism. We were a generation committed to throwing off the strangling conventions of the past.

We had been influenced by philosophers such as Wilhelm Reich, who urged sexual expression as a path to liberation, along with the new Marcusian Marxism that saw students as the revolution's vanguard.

Old hierarchies were to be smashed, the division between teacher and student dissolved, and in that heady atmosphere romantic liaisons abounded, not least because the expansion of the higher education sector brought in a new breed of lecturers barely older than their students. Love was in the air.

Nowadays, those brilliant young pioneers who are still in the academy are several decades older than their students. And even though a few renegades still sport jeans and greying ponytails, smoke the odd spliff and occasionally strum a Dylan tune on the guitar in the office, they are no longer likely to be caught in flagrante in the photocopy room.

For a start, they are probably too tired. Who has the energy to think about sex when confronted with an ever-increasing mountain of paperwork? And then there is the fear of disclosure, dramatised so starkly in David Mamet's play Oleanna, in which a college student accuses her professor of sexual harassment.

Oleanna was criticised by some feminists as part of the backlash that aimed to discredit women who "cry wolf". When Naomi Wolf, author of The Beauty Myth, claimed a couple of years ago that as a student in the 1980s she had been harassed by Harold Bloom, the distinguished literary scholar, some thought she did so to counteract this kind of prejudice.

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Others, though, regarded her public "outing" as mere self-publicity. Jenni Murray, presenter of Radio 4's Woman's Hour, regretted that Wolf had chosen to speak out at a time when young women needed strong role models who did not portray themselves as victims.

The row was exacerbated by the intervention of Mary Beard, professor of Classics at the University of Cambridge, who, at the height of the Wolf outcry, confessed to finding it "hard to repress certain wistful nostalgia for that academic era before about 1980 when the erotic dimension of pedagogy ... was firmly stamped out".

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What Beard didn't seem to acknowledge was the element of power at play between a male teacher and a female student.

Easily the most significant change in attitude since the carefree, sexually charged Sixties has been the emergence of women's liberation, which said the personal was political.

Feminist analysis allowed us to see that what we once regarded as liberation was often just another form of repression. As June Purvis, professor of gender history at the University of Portsmouth, puts it: "The wandering-hands fraternity used their status and power to exploit female students, and some were silly enough to feel 'flattered' by this attention."

Having been dean at two institutions, I've had to deal with several unpleasant instances of sexual harassment, as well as the occasional allegation that was not clear cut. I have even had students complaining about unfair marking because of a tutor's known involvement with a student.

What is sad about these cases is that they seem to be symptoms of an unhealthy malaise, a mistrust between staff and students that makes me look back with a certain wistfulness to my student days, so suffused with optimism, with such a sense of camaraderie and intellectual curiosity shared by faculty and students.

It's no wonder that those who still have the stamina or the foolhardiness to persist in campus romances rarely come clean. So you have to play dirty. Once, when a hot affair was scorching through media studies, I confronted the offender only to be met with resolute denial. So I grabbed him by the collar, pulled his face close to mine and snarled: "I know it's going on - so end it NOW or ELSE!"

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A year later, he told me he had been so terrified he had stopped seeing the girl. And she still got a first.