Dr Pat Sikes, who has been studying the subject of pupil-teacher relationships for 25 years, fell for her own history teacher at the age of 14 and later became his wife.

And she believes classroom affairs are more common than is usually imagined - backing one estimate that around 1,500 relationships develop every year.

Dr Sikes, a lecturer in education, argues recent changes in the law which have criminalised sexual relationships between pupils and teachers always make the student appear as the victim.

But under-18s can, in fact, often be the instigators of genuine relationships, she writes in her paper 'Scandalous Stories and Dangerous Liaisons: When Female Pupils and Male Teachers Fall In Love'.

But Dr Sikes argues that expressions of sexuality are part of the everyday exchanges of school life. "And nowhere more so, perhaps, than in the seductive nature and 'erotic charge' often characteristic of 'good' teaching which provokes a positive and exciting response," she writes.

NSPCC Yorkshire official Sue Woolmore said children spent a significant time in school and teachers had a unique position of trust with their pupils.

"Teachers have a responsibility to maintain clear boundaries for their own response to pupils' sexuality, by never exploiting their position of trust and crossing the line into a sexual relationship with a pupil."

ChildLine spokeswoman Natasha Finlayson added: "The Sexual Offences Act was designed with a welcome emphasis on protecting children and young people, rather than on the rights of the small number of pupils over the age of consent who engage in sexual relationships on equal terms with a teacher."

Teachers are usually banned from returning to the classroom altogether if found guilty of affairs with pupils. But Dr Sikes argues attractions between teachers and pupils do inevitably happen and can on occasion become overtly sexual.

Despite the taboo nature of resulting relationships, most people working in schools know of at least one case of a teacher and a pupil marrying or living together in an enduring and solid relationship.

"But there clearly are other kinds of relationships which do not fall into these categories - this is the taboo issue which I am seeking to open up for debate."

Included in her paper are details of an initially-platonic affair which began when a girl was just 13, and another in which a 17-year-old had a sexual relationship with her 35-year-old course supervisor.

"It wasn't until two years later, on the evening he left to take up a post elsewhere, that we declared our feelings. I returned after the summer vacation as his girlfriend," she said.

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