There is nothing like the lurid imaginings provoked by an affair between a teacher and a pupil to tap the national subconscious. Earlier this year, in the aftermath of the tabloid feeding frenzy provoked by the sad case of Amy Gehring, a Canadian teacher accused and subsequently acquitted of having sex with under-age pupils, a boy band called Busted made their way to number three in the pop charts, with a charming little number called “Miss McKenzie”.

Sung by a group of boys who were barely out of short trousers themselves - one was only 16 - it gloried in the salacious story of a boy’s affair with his teacher. Here is a taster: I love a member of the staff I fight my way to front of class To get the best view of her ass I drop a pencil on the floorShe bends down and shows me more After a bit more voyeurism at Miss McKenzie’s home, the hero of the story gets his girl, or 33-year-old teacher in his case, and drives off into the sunset.

The record is just one face of the British public’s schizophrenic attitude to sex with young people and, in particular, sexual relationships between teachers and their pupils. On the one hand Fleet Street - in particular the tabloid end of it - likes to scream at the top of its voice about the “pervert sirs” preying on youngsters. A casual comment by Chris Woodhead when chief inspector of schools that relationships between students and pupils could be “experiential” and “educative”, and revelations that he had a sexual relationship with a former pupil nearly brought his career to an abrupt close.

On the other hand, there appears to be something terribly exciting about the taboo. News editors will devote more space to incredibly detailed descriptions of the tossings and turnings of cases like Gehring’s than to the average murder. Articles, especially if they involve female teachers and male pupils, often trivialise the offence and make eager readers complicit in the offender’s behaviour in near pornographic retellings of their activities.

The Gehring case, for instance, produced descriptions like this in the Sunday Mirror: “She could not help noticing how tall and athletic the schoolboy was... It was not dirty or raunchy sex. He was loving, caring and sweet.”

The same paper, describing an earlier case involving schoolteacher Tracey Kearns and a 16-year-old pupil began with a quote from the teacher: “There was lots of sex. I have never known anything like it,” she said. “It wasn’t so much what I could teach him but what he taught me... I was surprised a lad of that age could satisfy me so much.”

Whatever the confusions of the public’s attitude to relationships between teachers and pupils, the consequences of involvement in such relationships for a teacher couldn’t be more straightforward. Quite simply, since the introduction of a new Sex Offences Act last year, any relationship with any pupil under the age of 18 could land teachers in prison.

Previously, teachers who had sex with pupils in their care were not committing an offence as long as the pupil was over 16. There was also variable enforcement of professional disciplinary standards relating to such relationships, with some heads allowing teachers to move to new schools after affairs had been discovered. Teachers can now expect an abrupt end to their careers even if their case does not reach court, with heads now instructed to supplement criminal record checks with thorough informal investigations of the backgrounds of new recruits.

Of course, there are many stopping-off points before a full- blown affair. Flirtations between teachers and older pupils have long been an everyday reality in sixth forms. Some teachers will claim flirtation is integral to their teaching technique.

But Ted Wragg, professor of education at Exeter University, advocates a zero-risk approach. He says: “It is quite flattering to find you have got a fan club of people who find you interesting and want to talk to you, whether you are male or female. I always warn my student teachers not to be flattered. You have to be mature about it and realise this is a professional issue.”

Professor Wragg tells trainees to beware not only of real entanglements but of giving the appearance of inappropriate behaviour. Unfounded allegations of impropriety have put the brakes on many a career and ruined some. Meeting pupils outside school or corresponding with them, for instance, can help foster a perception of unprofessionalism. In the worst case, they lay the teacher open to false complaints of inappropriate behaviour from pupils.

“Even in very innocent cases it is important to be very cautious nowadays,” says Ted Wragg. “What if a male teacher wants to tell off a female pupil after school? He may have very good reasons: he might not want to disrupt the class. However, the teacher must be aware of the real dangers of doing this kind of thing on your own. Accusations might be made that you will find it very difficult to defend yourself against. You need to find a private but semi-public space, like the corner of a library, where you can maintain privacy while being in sight of others.”

Perhaps the last word should go to Chris Woodhead. Asked in a recent newspaper interview how close teacher and pupils should get, Mr Woodhead recently said:“The short answer is, they shouldn’t get close.”