A Home Office researcher who wrote a report into the sexual exploitation of children in Rotherham has said she faced "hostility" from the council.
Her inquiries in 2002 indicated there were then more than 270 victims. Last week, a report revealed more than 1,400 were abused from 1997 to 2013.
The researcher accused the council of being involved in the unauthorised removal of information from her office.
But, the council said it had found no evidence of such allegations.
The researcher, who does not want to be named, told BBC Panorama the draft of her final report was sent to the Home Office and Rotherham Council on a Friday.
Stories 'so graphic'
That weekend, someone visited the offices of a youth organisation where she had been based, without permission.
She said there had not been a break-in, but: "They'd gained access to the office and taken my data, so out of the number of filing cabinets there was one drawer emptied and it was emptied of my data.
"It had to be an employee of the council."
The researcher had met the victims at a youth organisation called Risky Business, which had been set up by the council.
"The workers in that project were the only people that those young people trusted, that they were telling the complete story to," he said.
"And some of the stories that I heard very early on were just so graphic that I don't think I will ever forget them.
"I was collecting data on who the perpetrators were, what cars they were using, their grooming methods, their offending methods, and what I was also collecting, was information on professional responses."
When the researcher began to share her findings with the council, she told them most of the perpetrators being named were from the British Pakistani community.
She said she was taken aback by the response from one official.
"They said you must never refer to that again, you must never refer to Asian men," she said.
"And [the] other response was to book me on a two-day ethnicity and diversity course to raise my awareness of ethnic issues."
A chapter of her draft report contained severe criticisms of agencies working to tackle the abuse including "alleged indifference towards, and ignorance of, child sexual exploitation on the part of senior managers".
It also stated: "Responsibility was continuously placed on young people's shoulders rather than with the suspected abusers."
Her report was never published. And the council even tried unsuccessfully to get the researcher sacked.
She said: "I was subjected to the most intense personal hostility - there were threats made from a range of sources. I've never seen back-covering like it and I still feel extremely angry about that."
Prof Alexis Jay, who wrote last week's independent report into the abuse in Rotherham, said the Home Office report was "effectively suppressed".
Her report states: "Had this [2002 draft] report been treated with the seriousness it merited at the time by both the police and the council, the children involved then and later would have been better protected and abusers brought to justice."
'Punished for truth'
Prof Jay told Panorama: "The response was, in a nutshell, she was punished for speaking truth to power.
"If they had taken account of the content and been less concerned with their own images then a great deal more might have been done at an earlier stage."
Panorama also spoke to Dr Angie Heal, who was employed by South Yorkshire Police to investigate drugs crime in 2003. She quickly identified links with sexual exploitation.
"It really didn't make any sense as to why there weren't major police operations that were being launched to investigate these issues," she said.
She wrote a report that pointed to a lack of convictions and named offenders, which was sent to senior police officers and council managers, but nothing happened.
"There were issues of ethnicity, and some people felt that ethnicity was a barrier to investigating, that it was seen to be too sensitive an issue," she said.
Martin Kimber, chief executive of Rotherham Borough Council, said the authority had accepted in full the findings and recommendations made in Prof Jay's report.
However, in a statement he said: "The alleged "raid" on the Risky Business office is not something that I am aware of and having made appropriate checks within the council, I am unable to find anyone who recognises this series of events as they have been presented to us.
"Similarly, I have been unable to find any reference within the Alexis Jay report to the alleged incident and have no other independent means of corroborating the allegations that are being put forward. If further information is made available which enables me to do so, I would be happy to look into it."
In response to the allegations in the programme, South Yorkshire Police said it was "determined to bring offenders of child sexual exploitation (CSE) to justice" and had increased from 10 to 45 the number of officers involved in investigations.
"A number of large-scale investigations looking at historical and current sexual offences in Rotherham are ongoing and involve a large number of victims," it said in a statement.
"We would be compromising those investigations if we were to provide any more details at this stage."
The release of the report had prompted a number of new CSE allegations had been made, the force said, indicating victims had confidence they would be properly investigated.
Panorama: Stolen Childhoods: The Grooming Scandal is available to watch on the BBC iPlayer.