Renate Williams is accused of seducing the teenager while on a school trip. She denies the charge.

Her lawyer, Andrew Fisher, told Worcester Crown Court that Ms Williams had been place in a "difficult position" by a system which made it too easy for children to make false allegations.

In his closing statement to the jury, Mr Fisher said: "In a world where respect for teachers has almost totally disappeared, making allegations of sexual misconduct is easy because there are never any direct witnesses to events. Allegations such as these seem to be common."

Mr Fisher said it was "police practice" not to challenge children about what they alleged "even when it is known to be wrong".

He said: "It is never suggested that they are lying until it comes to court.

"But anyone who has dealings with children, as parents, teachers or whoever, knows that children can be mistaken, fantasise, or be open to the suggestions of others. This culture is terribly dangerous."

He said Ms Williams accepted it had been "inappropriate" to strip naked for a nighttime swim in front of her pupils, but she catagorically denied she had sex with the 15-year-old boy in question.

Earlier, the court heard that Ms Williams had lied to police about her midnight swim, claiming she had been wearing underwear - a statement she retracted later in court.

Nicholas Fisher, prosecuting, said Ms Williams was the only "proven liar" in the case.

Ms Williams, from Poole, Dorset, told detectives she was constantly propositioned and sexually harassed by pupils at the Worcestershire boarding school where she taught.

A separate charge of having sex with a pupil in her room at the school has been dropped after the boy admitted, under cross examination, that sexual intercourse did not occur on that occasion.