AN ASSISTANT headmaster who had a sexual fling with a schoolboy was last night starting a two-year prison sentence after a jury convicted him of eight charges.

Married father-of-two Adam Williams and the boy had kissed and performed sex acts on each other. They were eventually found out when the victim’s sister found incriminating text messages and pictures on her brother’s mobile phone.

After a jury convicted 35-year-old on all eight charges against him, Judge Julian Hall told him: “I have seldom seen someone in such complete denial of what you obviously had done.”

He added: “It was all your idea. You were the grown up.

“You can’t be a wimp. You must have a spine in you.”

Williams met the boy on gay networking site Grindr and the pair went on to exchange 6,500 text messages.

Williams, who taught at an Oxfordshire school, denied all of the allegations, claiming the messages were part of a “fantasy relationship” which the boy was blackmailing him into.

Jurors rejected Williams’ claims and returned guilty verdicts on seven counts of sexual activity with a child by an adult in a position of trust and one of being a person in a position of trust inciting a child to engage in sexual activity.

He was handed a two-year jail term on each count, all to be served concurrently.

During the trial at Oxford Crown Court, jurors had heard how the boy, who cannot be named for legal reasons, had initially lied about his identity and age on Grindr, despite using a genuine picture of himself.

Christopher May, prosecuting, said after a while Williams knew how old the boy was and it was at that point the relationship should have ended.

By choosing to continue, he broke the law.

In one text Williams was said to have told the boy that if their relationship became known, “the Daily Mail would love it”.

Mr May said: “There were seven meetings between the two where sexual activity took place.”

The barrister said it was a criminal offence for somebody who was in a position of trust to engage in sexual activity with somebody under 18.

Following the verdicts, Edmund Vickers, defending, said in mitigation: “If it can be described as such, there was an innocent start to the relationship but clearly there came a stage when that ought to have stopped.

“It clearly is the end of this man’s career.

“He will forever have to live with the shame.”

Williams, of Ruardean Walk, Cheltenham, will also have to sign on to the Sex Offenders Register for 10 years and be placed on the Safeguarding Vulnerable People register.

The boy’s mother said after the sentencing: “Our family life has been one of no joy or laughter for the last 10 months.

“Throughout this process I have personally felt helpless and the guilt you feel as a mother that you have allowed this to happen to your son will remain for the rest of my life.”

Louise Chapman, Oxfordshire County Council’s cabinet member for children, said: “Teachers hold an important position of trust.

“Mr Williams’ abuse of this trust is a matter of disappointment and concern. The sentence of imprisonment for offences of this kind is welcomed and supported by the county council”.