A 31-year-old PE teacher who repeatedly had sex with a 15-year-old boy 'over an extended period' has been banned from the classroom for life.

The boy later sent a threatening letter to disgraced Alexandra Sharman at about the time he confided to a GP that he was the victim of 'sex abuse'.

The family doctor told police about the behaviour of the teacher at Marriotts School in Stevenage - but her victim, identified as Pupil A, refused to press charges.

School: The family doctor told police about the behaviour of the teacher at Marriotts School (pictured) in Stevenage - but her victim, identified as Pupil A, refused to press charges

After receiving the threatening letter Ms Sharman told the school's former head of behaviour, safety and attendance - 'Witness B' - that 'lines had been crossed'.

She also admitted the relationship to her family and a fellow teacher, 'Witness A', before telling her former partner: 'I've had sex with a student.'

She was fired from the school - whose motto is 'Aim high. Work hard. Be kind.' - for gross misconduct after working there for more than eight years.

Ms Sharman was found guilty of unacceptable professional conduct and conduct that could bring the profession into disrepute by a panel of the National College for Teaching and Leadership.

The panel said the 'inappropriate relationship between Ms Sharman and Pupil A involved engaging in sexual activity including sexual intercourse more than once.

'Based on the totality of the evidence the panel are satisfied there was an intimate and sustained relationship between Ms Sharman and Pupil A over an extended period.'

The hearing in Coventry was told the relationship with Pupil A began when he was in Year 10.

Panel chair Ms Janet Draper said: 'The allegation came to light in approximately June 2015 when Pupil A disclosed to his GP that he had been the victim of alleged sexual abuse at the hands of Ms Sharman when asked why he was "depressed".

'Pupil A's GP passed this information on to the Hertfordshire Constabulary. On 20 June 2015, Ms Sharman spoke to a friend and school colleague, Witness B, about a threatening letter that she had received from Pupil A and the nature of her relationship with him.

'On June 21, 2015, Ms Sharman also told her friend and school colleague, Witness A about the letter from Pupil A and disclosed the nature of her relationship with him.

'On June 21, 2015 Witness B informed the headteacher at the school of the disclosure made to her by Ms Sharman.'

Ms Sharman was suspended on June 23, 2015. Pupil A was interviewed by police on the July 19, 2015 and said he did not want to make a formal complaint of a crime.

The school was informed by the police in December 2015 they would not be pursuing criminal prosecution against Ms Sharman.

Ms Sharman submitted a letter of resignation on January 12, 2016 before the subsequent school investigation had been completed.

Ms Draper said: 'The panel carefully considered the written statement provided from Pupil A.

'The panel approached Pupil A's evidence with great care and caution due to the manner in which he raised his relationship directly with Ms Sharman, namely the threatening letter he wrote to her, which gave the panel considerable cause for concern.'

Ms Sharman did not attend the hearing and did not want the NASUWT (National Association of Schoolmasters Union of Women Teachers) to represent her.

Ms Draper said: 'The panel considered Pupil A's statement and the various descriptions he had given of the sexual activity which took place.

'Having carefully considered the evidence before it the panel are satisfied that the inappropriate relationship between Ms Sharman and Pupil A involved engaging in sexual activity including sexual intercourse on more than one occasion.

'Based on the totality of the evidence the panel are satisfied there was an intimate and sustained relationship between Ms Sharman and Pupil A over an extended period.

'On June 20, 2015, Ms Sharman told Witness B about the letter she had received from Pupil A and disclosed that 'lines had been crossed'.'

The next day Ms Sharman told Witness A about it and confirmed the relationship.

Ms Draper said: 'Ms Sharman's ex-partner arrived later that evening and Ms Sharman told him about the letter from Pupil A and said 'I've had sex with a student'.

'Shortly after she repeated this disclosure to her sister and parents. Both these disclosures took place in the presence of Witness A.

'On June 21, 2015, Witness B spoke to Ms Sharman by telephone and told her she would be informing the headteacher at the school of the disclosure.'

Ms Sharman was prohibited from teaching indefinitely which means she cannot teach in any school, sixth form college, relevant youth accommodation or children's home in England.

Ms Draper said: 'There is no evidence Ms Sharman's actions were not deliberate and there is no evidence to suggest she was acting under duress.

'In fact, the panel found the teacher's actions to be calculated and intentional.'

Decision maker Jayne Millions, on behalf of Education Secretary Justine Greening, said the case was so serious Ms Sharman will not be allowed to apply for restoration of her eligibility to teach.