A major review to unearth failures to tackle grooming gangs has found that potential human error led to some police investigations being dropped.
The review - named Operation Beaconport - is looking into cases between 1 January 2010 and 31 March this year.
Thousands of cases are expected to come under scrutiny.
So far, 1,273 files from 23 police forces have been referred to the review, led by the National Crime Agency (NCA), of which 236 are being examined as a priority because they involve allegations of rape.
NCA deputy director Nigel Leary said initial reviews suggest there were mistakes in some investigations.
He said: "Initial reviews have identified that in some cases where there has been a decision to take no further action (NFA), there were available lines of inquiry that could have been pursued.
"We've seen in those cases what appears to be potentially human error."
Mr Leary said that in some cases the inquiries haven't followed what the NCA would characterise as "proper investigative practice".
"That includes, for example, lines of inquiry being identified but not being followed, victim accounts not being taken in a way that we would recognise as best practice, and suspects not being pursued or interviewed in the ways that we would anticipate," he said.
Read more from Sky News:
Hull grooming gangs investigation reopened
Officers taken off Hull grooming gangs investigation
Last month, the Metropolitan Police announced officers were reviewing 9,000 cases of child sexual exploitation.
It is expected that some of these will be referred to Operation Beaconport, which is looking at cases involving two or more suspects, more than one victim, contact offences, where the suspects are still alive, and that have not already been independently reviewed.
The investigation into grooming gangs and other non-familial sexual abuse in Rotherham between 1997 and 2013, Operation Stovewood, has cost £89m over 11 years. It is not clear how much the latest investigation will cost.
However, Mr Leary said it would be the "most comprehensive investigation of its type in UK history", with the NCA estimating thousands of officers will be involved in the overall operation.
Officials are recording the ethnicity of suspects and victims as part of the review, and have found gaps in the existing data that they are trying to fill.
As they examine cases, they aim to flag any dangerous suspects, and any that are at risk of fleeing the UK.
Investigators have vowed to be "honest and transparent" with victims from the start, to avoid giving them unrealistic expectations.
Richard Fewkes, from the National Police Chiefs' Council, said while going after perpetrators is important, some victims will just want to feel they are being listened to.
He said: "Justice means different things for different victims and survivors, and no one victim and survivor is the same.
"For some, justice is just being believed, perhaps for the first time, by someone in authority - being listened to.
"Or it might even be understanding that the review has taken place, a reinvestigation has taken place in an appropriate, focused, robust way, but nothing more can be done.
"For some that is justice in their mind."
(c) Sky News 2025: 'Human error' may have led to grooming gangs investigations being dropped, review says
Local news content from CItiblog - read more at
Zohran Mamdani: 'AND IT SO BEGINS,' says Trump - after his 'worst nightmare' celebrates New York election result
Kentucky plane crash leaves at least seven dead - with number expected to rise
Biggest schools shake-up in a decade to cut GCSE exam time - and add AI and fake news lessons
Will Rachel Reeves repeat Denis Healey's 1975 horror budget?
Number of female MPs could plummet for first time if no action taken
Mum issues Bonfire Night warning as number of children seriously injured by fireworks hits decade-high
Prince William wins hearts as he cuddles baby handed to him on Brazilian island
Reflecting sunlight into space could 'buy time' against global warming - but experts warn of 'rogue nations' risk