Scotland Yard has hit out at the BBC after it broadcast a Panorama programme focusing on the claims of a man who made allegations of child sex abuse by a VIP paedophile ring.
The Metropolitan Police issued a lengthy statement in light of the show which featured a man, known only as David, saying he may have been led into making the claims by campaigners.
The force said it had "serious concerns" about the impact of the programme on Operation Midland - its investigation into historical child sex abuse and murder - and any effect it may have on witnesses and the willingness of victims to come forward.
It added: "We have warned previously about the risks of media investigations compromising a criminal investigation. When we initially launched our Operation Midland appeal, we specifically highlighted how a media organisation - the BBC in fact - had shown pictures of individuals to 'Nick' which could compromise the evidential chain should a case ever proceed to court.
"We continue to be concerned about approaches to witnesses by all media, and that warning was reinforced by the Attorney General on Friday September 25."
In an appeal for witnesses when the inquiry first started, police described the main witness - known by the pseudonym "Nick" - as "credible".
It later conceded that using such language may have suggested it was pre-empting the outcome of the investigation, when that was not the case.
Responding to claims made on Panorama, the Met reiterated it would not be giving a "running commentary" on the progress of Operation Midland.
On the programme, David said he had provided the names of VIPs, including former home secretary Leon Brittan, "as a joke suggestion to start with", but that he later repeated them.
He 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, and is believed to have told police he was worried two well-known campaigners may have led him into making false claims.
But the Met asserted it had a responsibility to protect vulnerable victims and witnesses, and it was worried the broadcast would deter people from coming forward.
It added: "We recognise that there is a public interest in reporting and commenting on the police and our investigations. We can and do accept criticism of our policing operations.
"But we do believe there is a distinction to be made between fair comment and impacting on victims and witnesses in a way that may damage them or a criminal investigation."
Responding to the Met's criticism, the BBC said it was important that the conduct of police, journalists, campaigners, and politicians was examined.
A spokesman for the corporation said: "This is important and fair investigative journalism that rightly asks legitimate questions about the conduct of the police, journalists, campaigners, and politicians in handling historic allegations of child abuse.
"We were aware the Met Police has concerns about this Panorama going ahead but as they recognise there is public interest in reporting on their investigations."
He added that while the BBC had taken the Met's statement seriously, it had been issued before the programme aired.