A special needs pupil who allegedly had sex with a Mid Wales teacher in the toilets of the British Library threatened to assault his headmaster, a court has heard.

The boy, who was 16 at the time, made the threat after his teacher Teresa McKenzie, 39, of Meifod, near Welshpool, was suspended over concerns she was having a relationship with him.

McKenzie, who was deputy head and the boy’s key worker at the Cheshire school, denies seven counts of sexual activity with a child by a person in a position of trust.

The prosecution claim she had a 14-month affair with the teenager – who has a range of conditions including Attention Deficit Hyperactivity Disorder.

Yesterday Chester Crown Court heard the boy became aggressive when the married mother-of-two was suspended in May 2008.

A teaching assistant at the school told the jury: “He came up to me and said if Teresa wasn’t back in school he was going to kick my head in and kick the headmaster’s head in as well.”

Asked by Mr Simon Mills, prosecuting, how he was when she wasn’t around, the witness said: “He was very lost. He was very abusive towards staff and pupils. He didn’t really like anyone else talking to Teresa. If anyone approached her he would become very abusive and aggressive.”

Another teacher recounted a time she walked in on the pair in a classroom.

She said: “They were in there with the door closed. When I opened the door they moved apart quickly. This was about spring 2008 but it was going on so long I am not sure which year it was.”

Mr Tim Roberts, for McKenzie, said to the teacher: “Mrs McKenzie had to have counselling sessions with him, one to one, privately every day. Did you know that?”

“No,” answered the witness.

It is claimed McKenzie, formerly of Chester Road, Tarporley, had sex with the boy in her car, in his home and in a London hotel.

The complainant has already told the court the pair had sex several times in disabled toilets at the British Library in London.

The court has been told the boy had previously invented a string of relationships and sexual encounters and accused family members of sexually abusing him.

The trial continues.

By Anwen Evans