Ick. This, roughly, is the appropriate response to the news that a teacher is sleeping with a sixth-former.

The degree of ickiness might vary with the teacher’s age: few people would disagree that a 52-year-old sleeping with a 17-year-old, for example, is very icky.

But it is not paedophilia.

An adult who wants to have sex with a four-year-old child is very, very sick. An adult who wants to have sex with a 17-year-old teenager is not sick at all. Or at least not in a dangerous, paedophile way.

And this is where the ickiness comes in. Because there is, of course, something wrong with any sexual relationship between a teacher and a pupil at the same school.

The pupil might be attracted to the teacher’s power and authority, or feel special when singled out for attention. The teacher might like having a sense of superiority and control over a pupil-lover.

None of this is particularly healthy. But if we were to legislate against all power-play and inequality in relationships, half the country would be in jail.

For most people, the choice to pursue an unhealthy relationship is up to them, their partners, and any of their friends forced to suffer through the pub-based moaning sessions.

But teachers can be put in jail for it. They can have their names added to the sex-offenders’ register. We should not sanction abuse of power in any context. Teachers who have affairs with pupils should be subject to strict professional disciplinary procedures.

But jailing them for their messed-up relationships does nothing to help protect vulnerable children against the advances of genuine paedophiles.