Should the Met 'believe' victims from the outset?

"Credible and true" - three words that have resulted in nine months of criticism for the Metropolitan Police.

They were used by a senior police officer to describe allegations that have either lifted the lid on a paedophile ring at the heart of the establishment, or needlessly tied up nearly 30 police officers and demolished the reputations of pillars of the community - depending on whether evidence is found. This is work in progress.

The man behind the allegations is in his 40s and has given detailed evidence to police working on Operation Midland that he was controlled by the paedophile "group" for nine years until the age of 16. He says three boys were killed.

Detectives used to investigating murders have described him as credible. His allegations are incredible or at least difficult to believe.

To be true, they require a conspiracy between at least a dozen men including senior politicians, decorated military leaders and security service chiefs.

Drivers and minders would have to have turned a blind eye to the delivery of children to distinctly adult environments, and parents would have to have either been complicit, hoodwinked, or so badly abused themselves that they didn't report the regular absences of those children.

Yet at the start of their inquiry, detectives said the story was "true".

That, the Met has now accepted, gave the impression that police were pre-empting the result of an inquiry that may end in the decision that there is no, or not enough, evidence to justify further action. "We are not," the Yard insisted, "we have open minds."

So why say it in the first place?

The answer might be found back in the autumn of 2012 when the Met briefed the media that it believed the late Jimmy Savile had been a "predatory sex offender", who had abused children on "a national scale".

The offender was dead, and the investigation had barely started, but the reaction electrified the inquiry. Women and men came forward in large numbers to accuse Savile, and together they presented a strong case that, as the senior investigating officer, Cmdr Peter Spindler, later put it, the entertainer had "groomed a nation".

It encouraged disclosure from those who had not revealed they had been a Savile victim because they could see the police appeared to be taking seriously the allegations of abuse, even "believing" them from the outset.

An officer investigating another allegation of child abuse in the past has told the BBC there is nothing unusual in this.

He describes telling another alleged victim he had recently interviewed that he "totally believed him". He said: "Police 'believe' all our victims and they are told this so they will continue to engage with us."

All this follows decades during which the Met has accepted police often did not believe victims, however credible. But the deployment of "true" as a police tactic in Operation Midland has resulted in a swing back towards the view that potentially false stories are being entertained with big police inquiries.

Operation Fairbank - the Met's umbrella inquiry into historical claims involving politicians and other public figures. It began in 2012 as a "scoping exercise" to establish evidence for formal investigation and went on to establish a number of criminal investigations:

Key investigations across the UK

Operation Midland has 27 officers, though not all such inquiries are as large.

The BBC understands a recent investigation of historical child abuse in Suffolk was shelved after a single detective, who worked on the case for several months, uncovered evidence that contradicted the allegations.

Despite that, the former Director of Public Prosecutions, Lord McDonald, says the police service has gone so far in the opposite direction it has "lost its sense of balance".

"The fact of investigation becomes conviction in itself," he said. "[That has] resulted in the untrammelled trashing of the reputations of those who are dead."

As a result, there is likely to be increased support for those accused of sexual offences to be given anonymity, at least to the point where there are charges. Alleged victims are already protected.

The Commissioner of the Metropolitan Police, Sir Bernard Hogan-Howe, has said it is something he would support.

Meanwhile, Operation Midland continues. Scotland Yard says its detectives will continue to believe their witness "until we identify reasonable cause to believe otherwise".