John Walker used his position as a teacher and chess coach at school to isolate children and then sexually abuse them, police said.

None of the children he abused knew there were other victims -- he told them they would not be believed.

He also built up friendships with parents of his victims who were shocked to discover years later what he had done to their children.

Walker, 58, is one of Oxford's leading chess experts. He was chairman of both the Oxfordshire Chess Association and Oxfordshire Junior Chess Association. He coached junior chess teams and wrote books on the game aimed at children.

The former draughtsman with the Oxford-based Pressed Steel Company was also a prominent member of Oxford City and Cowley chess clubs.

But he concentrated his paedophile activities on his school pupils. No complaint against him came from those he coached in the city's chess clubs.

He molested children in his car during after-school activities, including football and chess, and during school trips.

Police, who focused their inquiries on contacting Walker's favourite pupils, successfully prosecuted him on 35 counts involving 19 children, but the final total may never be known. The victims were 11 years old or younger when he started abusing them. Some were abused for a year or more.

Dc Steven Hart, from Oxford police's family protection unit, began investigating Walker in September 2000 after receiving separate complaints of abuse from two people.

It quickly became clear Walker had interfered with many more pupils over the years.

The Crown Prosecution Service brought charges relating to 12 boys and seven girls.

Walker started teaching in 1974. The allegations centre on his second school where he worked between September 1976 and August 1989.

He then moved to Rye St Antony School, Oxford, from where he was suspended on his arrest on November 1, 2000. He later left by mutual agreement.

John Mitchell, spokesman for the county council's education department, said in a statement: "He was employed by us as a teacher between April 1974 and August 1989. We have helped police with their inquiries."

Walker's chess career took off with a win at the British Chess Federation's annual congress when he was 23.

But in later life he became more distant from the game and friends say he had not played actively for ten to 15 years.

He told the Oxford Mail more than 20 years ago: "I find that chess has a great appeal to many kids around the age of ten.

"If they learn enough to get keen, then it's an excellent way to keep them happily occupied in their free time.

His activities have come as a complete shock to his friends in the chess world.

Treasurer of the Oxfordshire Chess Association Tom Williams, 64, has known Walker for almost 49 years.

Mr Williams said: "He was a respected teacher for years and years and this relates to things that happened 25 years ago. I'm not aware of a single junior chess player that is involved.

"This man is going to go to prison for years and years and I simply can't believe he is guilty. It's a real shock to me."

He described him as a shy man in his youth who married a Russian woman when he was in his late 40s.

Secretary of Cowley Chess Club, Lester Millin, said: "He took groups to the British chess championships. All the people I know he took are absolutely amazed."

Witney Chess Club secretary Nick Jones, 49, has known Walker since he joined Cowley Chess Club at the age of 13 and was coached by him.

"I'm someone who started as a junior but when John was still quite young and coaching juniors.

"There was not an inkling. My personal feeling is extraordinary surprise," he added.