Britain's top police officer Sir Bernard Hogan-Howe has spoken of a "moral crisis" as he announced a judge will probe the controversial handling of claims of a VIP paedophile ring in Westminster.

The embattled Scotland Yard boss has called in former High Court judge Sir Richard Henriques to independently review how abuse claims against public figures were conducted by Met officers.

The Metropolitan Police Commissioner on Wednesday again refused to bow to calls to apologise to Lord Bramall amid fierce criticism over the conduct of Operation Midland, which saw police raid the home of the former D-Day veteran.

The case against him was later dropped.

Sir Bernard said Operation Midland would come to an end "at some point" but for the time being inquiries continue as the independent review gets under way.

He said: "Let's bear in mind, investigating historical child sex abuse is very difficult.

"We've had quite a moral crisis over the last 18 months where initially it was said that very senior members of government had lost dossiers, that they themselves were subject of allegations and now, here we are the very obverse of that criticism, that in fact we weren't ignoring things we have gone too far.

"Well surely it's right that someone should look at that and try and produce some balance and perhaps give some guidance about how police officers and others approach difficult, historical allegations where the evidence sometimes is lost, where people's memories have sometimes faded, and it's so easy to make allegations but then how do we prove them?"

Operation Midland, which had cost £1.8 million as of November last year, has come under intense scrutiny in recent weeks after the Met announced Lord Bramall would face no further action over historical child abuse allegations.

But amid a clamour calling for the Met boss to apologise, Sir Bernard said his men were only doing their jobs.

He said: "I can't apologise for carrying out an investigation into a serious allegation.

"Well , that's our job that's what we are here to do.

"I have already expressed, as we have, regret about any distress that we have caused to him and his family.

"I think a good next step is for Sir Richard to look into the concerns that Lord Bramall has expressed, and others have expressed, and let's get to the bottom of whether they are things that when we know all the facts, are valid and if they are, let's acknowledge it and if they're not, then let's say it."

"I have said at the right time I'm quite happy to see him. I think it has to be at the end of Operation Midland and perhaps at the conclusion of what Sir Richard may consider."

And Sir Bernard also denied any link between the review being announced and the shelving of the whole Operation Midland inquiry.

He added: "The inquiry will come to an end at some point but I thought this was an important time to actually have this review to be started now.

"I think what it is a sign of is there's been a lot of public concern, the newspapers have been full of criticism over the last few days and last few weeks.

"I've got things I need to be re-assured about, as do the public, but equally if the officers have done the right thing, for the right reasons, surely we all need to understand that's what's happened too.

"And one of the great dangers, difficulties we have, is that in our investigations we get lots of information, which we cannot put in the public domain. The officers have that information, so surely someone independent needs to look at that and that's the reason I have asked for this review."

Key findings of the review will be published later in the year, although the full report will remain confidential.

Operation Midland centred on claims that sex parties were held at the exclusive Dolphin Square apartment block near the Houses of Parliament.

Allegations by a man known as "Nick", were also made involving claims of the murder of three young boys.

At the time a detective described Nick's account as "credible and true".

Former Tory MP Harvey Proctor, who furiously denied any involvement and claimed he was the victim of a homosexual witch hunt, has been interviewed under caution twice but has not been charged.

Former prime minister Edward Heath and ex-home secretary Lord Brittan, who are both now dead, have also been named in connection with the probe.

But when the Met announced 93-year-old Lord Bramall would face no further action, calls for an apology grew and questions were raised over the veracity of Nick's claims.

Scotland Yard has already come under fire over its handling of a separate allegation that Lord Brittan raped a 19-year-old woman known as "Jane" in 1967. He died in January last year without being told he would not face action over the claim, made to police in November 2012.

In October police apologised to Lord Brittan's widow, saying she should have been informed there would not have been a prosecution had her husband been alive in April this year.

Lord Bramall's solicitor Drew Pettifer said: "Lord Bramall welcomes any review that can assist the police in making improvements in the way they investigate such allegations, thus making the process fairer and less painful for all those concerned."