Although his local education authority was warned of his conduct in 1989 and he was forced to leave the school, he was able to teach at a private school for a further 11 years until November 2000, when allegations about his conduct came to light.

Last month Walker pleaded guilty to 35 counts of indecency against children when he appeared at Oxford crown court. It was ordered that a further 20 charges lie on file.

The court heard that Walker, who at the time of the offences was single and lived with his mother in Headington, Oxford, picked his "favourite" pupils and then assaulted them in his classroom, in his car, in the changing rooms or at his home.

The victims were aged between seven and 13 years when they were assaulted at the school, which cannot be named for legal reasons. For some pupils, the abuse carried on after they had left the school.

Walker ran extracurricular chess and football classes and helped out at summer camps to gain access to pupils when they were alone, the court heard.

Sandy Stansfield, prosecut ing, said: "Walker abused both boys and girls, he had his favourites who were either in or out. One victim recalls Mr Walker being superficially friendly and having favourite pupils. Others he used to bully and humiliate."

The court heard that during holiday summer camps, Walker would lead children on midnight walks through graveyards, single out his victims and then sexually abuse them.

He abused others after chess lessons in his study at his home, or in the changing rooms after swimming.

Many of Walker's victims travelled to Reading to see him jailed; one shouted "rot in hell".

Afterwards, Detective Constable Steve Hart of Thames Valley police, said: "The witnesses have shown tremendous courage in coming forward and giving evidence against this man, who preyed on young children and was an immense danger to them."

Alison Jones, headteacher of Rye St Antony school in Oxford, where Walker worked from 1989 until 2000, said: "Mr Walker was an extremely competent and well respected teacher who produced excellent results ... We never had any problems with him and certainly no allegations of abuse were ever brought to my or my staff's attention.

"Prior to hiring him we carried out our usual checks with the Department of Education and the police and there was nothing at all to indicate anything untoward."

Jailing him for seven years, Judge Christopher Compston told Walker: "The children were very, very young and indeed it's quite clear you must have chosen those in awe of you as you were their school teacher."

Walker was permanently disqualified from teaching children, and placed on the sex offenders' register for life.