Nigel Oldfield, 46, was head of science at a Derbyshire school in the summer of 2002 when, over a three-week period, he collected pornographic images in several 18-hour internet sessions.

He came to the attention of the police when he was seen at a Sheffield shopping centre, allegedly taking pictures of children. When questioned, he admitted his home computer contained indecent images of youngsters.

Police later found he had collected 11,000 pornographic pictures and videos of all age groups, including babies. He served seven and a half months in Doncaster prison.

Senior managers at Doncaster College say they had no idea that the man studying a part-time law and criminology degree was himself a convicted offender. This is despite the fact that, last year, he appeared on the BBC’s Newsnight to discuss the treatment of child pornography offenders. He also came to public attention after setting up a web forum to support those accused of the crime, a story which was covered by national newspapers.

Mr Oldfield, regarded by police as unlikely to commit the offence again, says he has never been accused of any kind of physical assault.

He spent most of his time at the higher education campus, set on 126 acres of countryside in High Melton, but also studied at The Hub, the college’s central Doncaster FE site.

In February, an essay he submitted raised the suspicions of senior managers, who carried out an internet search. It revealed newspaper stories mentioning his past. His tutor, in a document submitted to the college, said he was concerned because Mr Oldfield had adopted a “political stance” which argued for a distinction to be drawn between different kinds of sexual activity involving children.

According to internal documents, which have been seen by FE Focus, senior managers decided there was a “high risk” of Mr Oldfield coming into contact with children, either teenage students at Doncaster College or toddlers in its creche.

In April, it was decided to exclude him from the college. He was also banned from the grounds after visiting the property to stage a one-man protest. Mr Oldfield has appealed against the college’s decision.

A hearing was held about his case on Monday and a further hearing is planned before the college makes its final decision.