A social worker who committed a string of sex attacks on children was allowed to carry on working for years after concerns about his behaviour were first raised.

Gordon Oliver worked in a senior position in Brighton social services until 2004 - four years after his colleagues warned bosses they were worried about the attention he was lavishing on teenagers in the department's care.

Oliver, 58, who lived in Washington Street, Brighton, was sentenced by Leeds Crown Court to five years in prison last week for sex assault charges going back as far as 1979 and possession of hundreds of sick pictures of children.

He was cleared in an internal inquiry in 2000 and formal advice warning him to avoid close contact with children was not put on his file.

An investigation by The Argus has revealed he was even allowed to have a child staying at his home on a temporary foster placement after he returned from suspension.

Oliver's 25-year reign of terror over victims from Yorkshire and Brighton ended in 2004 when police finally caught up with him.

Brighton and Hove City Council said last night it was unable to watch over its staff all the time and "had expectations" that they would conduct themselves professionally.

He was convicted of abusing five children, including a Brighton boy he groped during swimming sessions after being allowed to return to work.

The boy's grandmother said: "For 20-odd years this man put children in his care at risk. It is just appalling.

"It has completely messed my grandson's head up. He is afraid to trust anyone any more.

"People should know this can happen with social services."

One of Oliver's colleagues today accused Brighton social services of negligence and told The Argus the boy could have been protected if warnings from at least three social workers and a headteacher had been taken more seriously.

Brighton and Hove City Council, which took over social services from East Sussex County Council in 1997, announced it had set up a victims' hotline as it emerged Oliver could have abused dozens of other children.

Oliver's former colleague said: "The child he was charged over was just one of a number of boys who he was having sessions with, either swimming or spending time with. Potentially there could be a number of other children. It could go back years.

"I just find it unbelievable this was happening years afterwards without any manager saying, what is this guy up to? He was suspended following the allegation by the headteacher in 2000.

"When he was reinstated he was told he should be very careful about his boundaries. That was totally disregarded. He was in a position to abuse a child about two years ago "If they had followed proper procedures, this boy would not have been abused. There were at least three social workers who expressed concerns about his behaviour. Somebody has got to be held to account."

Oliver worked as a social worker in Bradford and most of his victims there are now in their 30s.

He began work in Brighton in the early Nineties and as a manager was not expected to have direct contact with children. But colleagues began to notice he was taking children swimming, accompanying them on holidays and inviting unchaperoned boys into his office and out in his car.

In 2000, the headteacher of a boarding school accused Oliver of inappropriately visiting a boy, taking him out and going over the boundaries of a normal relationship.

Oliver was suspended from his job as fostering manager while his superiors investigated. Despite at least two of his colleagues coming forward to echo the concerns, he was reinstated after about three months. Investigators had come to the conclusion he was very committed to children and did not have much of a life outside his work.

In 2001 concerns were raised about Oliver's conduct with another child.

Oliver had a Mercedes convertible and was driving the boy around in it.

His former colleague said: "He targeted kids who were particularly vulnerable. In 2001 he used to drive around with this boy. There was something really worrying about the way they seemed to relate to each other.

"Social workers don't go out of their way to work with kids on weekends."

The social worker believed Oliver managed to dupe colleagues and the department because he had such a pleasant manner and was well-liked. His former colleague said: "I think there was negligence by management. There was nothing on the supervision records to say he shouldn't be lone-working with children or taking children swimming. His line manager said she had no idea.

"She didn't realise it was anything to worry about, spending so much time with children on his own."

Police began to investigate Oliver after the Brighton teenager's grandmother became suspicious and complained to social services. Officers discovered hundreds of photographs of the boy at Oliver's home.

The pictures were seized but the police returned three weeks later to find more photographs of the same boy.

Oliver was suspended and then dismissed in 2004 after the police alerted his bosses.

Brighton and Hove City Council has admitted failing to pass on details of the warnings it gave to Oliver to his future bosses. A spokesman told The Argus: "Concerns were expressed about Gordon Oliver's conduct in 2000. "These were taken very seriously, and Mr Oliver was temporarily suspended while we investigated.

"Suspension is a neutral act and is standard practice when serious concerns are raised. We spoke to both the staff and to the young people involved. We found the evidence we got was based on gut feeling and speculation - not the sort of hard evidence that could have led to disciplinary action.

"We did however warn Mr Oliver about the concerns that had been raised, and we did set limits on his professional conduct. Between this period and 2004, when the police notified us of their investigation into Mr Oliver, we had no further concerns raised about his conduct.

"We immediately suspended him as soon as the police got in touch with us in 2004. During the subsequent investigation into his professional conduct we found evidence that he had been in act been transgressing the boundaries of appropriate behaviour while misleading management through his record keeping. So we dismissed him.

"We cannot watch over all our staff all the time and need to have expectations of professional conduct. In all social services teams there always has to be a balance between supervision and trust. However if someone sets out wilfully to deceive it can be very difficult to uncover." The council commissioned an independent review of its management systems which it said would "minimise the chances of this sort of deception happening again."

The council's Oliver hotline can be telephoned on 01273 295973 on weekdays from 9am to 1pm.