VIP paedophile inquiry: Police criticise Panorama broadcast
The BBC's decision to air a Panorama programme on child sexual abuse has been criticised by the Metropolitan Police, which says the broadcast could affect inquiries.
It said it had "serious concerns" about the programme's impact on witnesses and victims considering coming forward.
A man who made allegations against VIPs told Panorama that campaigners may have led him into making sex abuse claims.
The BBC said it was "important and fair investigative journalism".
However, Norfolk Constabulary chief constable Simon Bailey, who oversees child abuse investigations for the National Police Chiefs' Council, told BBC Radio 4's Today programme Scotland Yard was "absolutely right" to express concern publically over the programme.
In a statement that referred to the Panorama programme, called The VIP Paedophile Ring: What's the Truth?, the Metropolitan Police warned: "Seeing an individual make allegations and then be targeted by the media is not going to encourage others to speak out."
A man - who Panorama referred to as "David" - told the programme he had felt pressured by others to provide police with VIP names, including that of ex-Home Secretary Leon Brittan.
His account was the basis of news reports about the late Lord Brittan, who died in January 2015. Police investigated his claims but brought no charges.
By Danny Shaw, BBC home affairs correspondent
This is the third time in three weeks that Scotland Yard has warned that media coverage of Operation Midland could undermine its investigation.
Police are concerned that public scrutiny of victims, who've had the courage to come forward, could make them more vulnerable and lead them to withdraw from the case or put off other potential witnesses.
There's also the worry that journalists conducting parallel inquiries into the abuse claims could taint the police investigation, diminishing the chances of a successful prosecution.
The more cynical-minded might see the Met's warnings as a way of preparing the ground and getting its excuses in before making a decision to close the investigation.
But the force says it still has "lines of inquiry" to pursue and the Crown Prosecution Service will determine whether charges should be brought.
The Metropolitan Police also warned of the "the risks of media investigations compromising a criminal investigation", adding: "We continue to be concerned about approaches to witnesses by all media."
The statement said police would not be giving "a running commentary on the progress of our investigation".
Ceri Thomas, Panorama's editor, said: "We were enormously concerned throughout not to do anything that would deter victims from coming forward.
"But we think we have to be able to scrutinise how the police go about big investigations like this and there really isn't a way to do that without looking at the way that police have treated statements from victims and treated the evidence they've brought forward."
Find out more
What's the truth about the VIP paedophile ring by Panorama editor Ceri Thomas
Searching for the truth about child abuse by BBC home editor Mark Easton
Lord Brittan claims unreliable - 'victim' by Daniel Gordon, BBC Panorama
Peter Saunders, from the National Association of People Abused in Childhood, said child abuse was an "extremely difficult" crime to prove because it happens "behind closed doors".
He said abuse victims were "fragile people" and it was normal that memories were sometimes "not 100%".
"I could say to you the bedroom where I was abused has blue wallpaper, I could be wrong, it could have been red wallpaper - but that doesn't detract from the fact that it happened," he said.
Referring to the allegations against Lord Brittan, he said: "Under no circumstances would we wish anybody who is innocent to come under scrutiny or have their reputation trashed."
"David" spoke to Panorama as part of its investigation into the so-called Westminster paedophile ring, which is said to have murdered three boys in the 70s and 80s.
The late Lord Brittan was one of those accused of being part of it.
Lord Deben, a friend of Lord Brittan, told BBC Radio 4's Today programme that police did not tell Lord Brittan before he died that they were not going to pursue one of the allegations against him.
"These are terrible, terrible allegations and they ought to be pursued very, very toughly but in private until you know that you have sufficient allegation to make it a real possibility," he said.
Norfolk Constabulary chief constable Simon Bailey said an "unprecedented number" of abuse victims had approached police since the allegations about Jimmy Savile in 2012.
"I would not want those victims to now feel that if they do come forward and they make those reports that their lives will then be subjected to the type of scrutiny and type of exposure that we have seen in the recent weeks and months," he said.
"It's only right in my view that we should be given the opportunity to investigate."