South Yorkshire Police knew hundreds of young girls were making claims of sexual abuse in Sheffield but did not act, an ex-police officer has alleged.
Documents and interviews with ex-officers suggested the force failed to pursue a number of child sexual exploitation (CSE) inquiries.
It also ignored intelligence that girls as young as 12 were being raped and assaulted, the officer told the BBC.
The force said CSE inquiries were complex and could take a long time.
Two former senior officers are being investigated by the police watchdog over their handling of CSE allegations in Sheffield.
Threats to kill
A copy of a document from South Yorkshire Police's intelligence database details more than 200 girls in Sheffield who were suspected of being sexually exploited.
It also lists more than 320 men accused of carrying out abuse, mainly between 2007 and 2010.
The abuse includes:
- Dozens of allegations of sex with a child
- Physical assaults, including beatings
- Child abduction
- Threats, including threats to kill parents and threats to scald girls by holding kettles of boiling water over them
Most of the girls are aged 13 to 15 but some are as young as 12.
The nationalities of the alleged abusers include a mixture of Iraqi Kurds, white British, black British, and Pakistani Heritage, among others.
The document lists three members of the same family linked to the alleged abuse of almost three-dozen girls.
In most cases there is no evidence police took any action.
Ann Lucas, who set up and ran Sheffield council's sexual exploitation service until 2012, said she recognised some girls and many alleged perpetrators in the file.
She said: "This is a snapshot of some of the victims we had [worked with] over a number of years, but not every victim is on the document you've shown me."
"The information [we were getting]... was routinely passed in to the police. There was no way they could not have known."
'Most vulnerable' people
Some of the abuse claims detailed in the document were investigated and prosecutions did follow.
In 2007, one investigation known as Operation Glover led to the conviction of a group of Iraqi-Kurdish men - two of whom received 10-year prison sentences while two others received substantial custodial sentences.
Following that investigation at least two detectives urged senior officers to continue enquiries.
Other girls had been identified, allegations had been made, and new potential perpetrators had been pinpointed.
A 2007 report sent to several senior officers described an "emerging criminal issue" in Sheffield, saying the level of criminality was "serious", and the victims were "among the most vulnerable in society".
It also said South Yorkshire Police did "not have any effective process or policy to combat the situation".
Among the senior officers who were sent the 2007 report were Jon House and Paul Broadbent - according to Tony Brookes, who had worked as a detective on the investigation.
Both have now left the police but are the subject of Independent Police Complaints Commission (IPCC) investigations over previous allegations they failed to act on child sexual exploitation claims.
Despite the substantial problems identified, the team was disbanded.
Mr Brookes told BBC News: "The size of the exploitation was massive in Sheffield.
"We offered to form a unit to continue the work - we offered to advertise our work so girls would come forward. We were told, 'it's not going to happen, return to your districts.'"
Mr Brookes said he was called to a meeting with a still-serving officer to discuss what to do with the intelligence they had on other girls.
"He said to me, 'go and spend an hour or two with each girl and find out what's happened to them and tell them there's not enough evidence to go on."'
Mr Brookes, who retired last year after 30 years' service, said he refused to carry out the order.
The force's priorities at that time were mainly crimes including robbery, burglary and car crime due to mandatory targets set by the Home Office.
In 2009, Sheffield City Council raised further concerns about the extent of abuse and trafficking in the area.
The council asked police to start a new investigation and paid the force £50,000 towards the costs of Operation K-Safe, the BBC understands.
A team of four detectives began investigations and arrests were made. But within months, two detectives left the team and were not replaced.
In 2010, one of the force's most experienced analysts, Gary Birchall, was asked to report on the operation.
He concluded a full investigation should be launched given the level and type of criminality detectives had identified but it never happened.
Mr Birchall said: "I got a call telling me the operation's been shelved.
"I said it can't be shelved, there's evidence here that children are being trafficked, being sexually abused. There isn't a superlative that describes how I felt then or how I feel now. Utter, utter, disbelief."
'Wrong and misleading'
South Yorkshire Police said some of the intelligence gathered as part of Operation K-Safe eventually led to Amanda Spencer and Ian Foster being jailed last year for 12 and 14 years respectively.
Arrests and investigations could only go ahead when there was sufficient evidence, the force said in a statement.
It added: "We have developed strong processes to ensure all information and intelligence received about sexual exploitation is collated, shared with partners and reviewed on a very frequent basis to see if any further action can be taken."
Jon House, who is now a senior manager with consultancy firm PWC, told the BBC: "Any suggestion that I did not support investigations into CSE is wrong and misleading.
"I will respond to the IPCC and look forward to the full facts being established."
Paul Broadbent, who is now the head of the Gangmasters Licensing Authority, said: "It would be wholly spurious and wrong to say that I did not support allegations or investigations into child sexual exploitation in Sheffield.
"I very much welcome and will fully cooperate with any independent investigation."