MORE revelations are due to come out about historic Westminster child abuse allegations, an MP has warned.

Simon Danczuk spoke out yesterday after the Cabinet Office released a forgotten MI5 letter about a politician with a “penchant for small boys”.

Written by then-head of MI5, Sir Anthony Duff, the 1986 note made no reference to child safety but concluded that the unnamed MP had denied the allegation, adding that “the risk of political embarrassment to the government is rather greater than the security danger”.

Apparently “overlooked” during a 2014 Home Office investigation, it has now been published in a supplement to a review on whether the government covered up abuse allegations in the 1980s.

Many of the fresh files were discovered in a cache of “assorted and unstructured papers”.

Review author Peter Wanless, of the NSPCC, said no evidence of the deliberate removal or destruction of documents had been found and the new documents did “not necessarily” indicate a cover-up.

However, Labour MP Danczuk yesterday said: “These explosive papers show what I’ve long suspected – that the full weight of the British Establishment, including MI5, colluded in a cover-up to protect politicians who sexually abused young boys. That we can now see in black and white that the risk to children was not considered at all and the Establishment was more worried about the risk of political damage to the government is a damning indictment of the shameful attitudes of the people running the country at the time.”

New Zealand High Court judge Lowell Goddard, who is heading an inquiry into historical child sex abuse in England and Wales, is set to start again from scratch.

Yesterday, Home Secretary Theresa May ducked reporters’ questions regarding whether she had asked senior MI5 officials to explain Sir Anthony’s note, with its disregard for the abuse of children. May repeatedly said the issue would be a matter for the Goddard Inquiry.

Danczuk, pictured, who recently revealed that his campaigning work on child abuse has led to depression, said: “It’s vital that we understand why these papers did not feature in the original Wanless Review. I am sure more revelations will follow and we need to give Justice Goddard a free rein to uncover every aspect of this ugly scandal.”

The new material also includes documents about former Home Secretary Leon Brittan, Sir Peter Morrison, who was an aide to Margaret Thatcher, ex-minister Sir William van Straubenzee, and former diplomat Sir Peter Hayman – but the contents have not been released. All four men are now dead.

The MI5 letter was addressed to then-Cabinet Secretary Sir Robert Armstrong and Wanless said the comments were a “vivid example” of “misplaced priority” running to “the highest levels of government”.

He said the findings reinforced his view that child sexual abuse allegations had been given “considerably less serious consideration than would be expected today” and called the discovery of the new material “unhelpful” for public confidence.

Speaking on Radio 4’s Today programme, Wanless said: “People simply weren’t thinking about crimes against children, and the consequences of those crimes, relative to other considerations such as national security and the reputation of departments and individuals.”

Tom Watson MP, who has also campaigned on the matter, said “everyone knows to a greater or lesser degree” that collusion to protect “very powerful people” did take place, adding: “The Goddard Inquiry now has to make sure they get access to all these files and all these documents, not just the Cabinet Office documents but other departments that may have – as the Cabinet Office euphemistically described – unstructured files, ie, ones that have been missed in previous enquiries.”

The inquiry is not expected to report until 2020 and earlier this month it emerged that police are currently investigating claims that a serving senior Labour MP abused vulnerable children and young people for more than a decade.

The investigation comes after a Tory politician contacted detectives about the man.

Yesterday, Andi Lavery of child abuse survivors group White Flowers Alba, hit out yesterday over delays to revealing the historic documents but stressed that any current links between powerful figures and abuse must be investigated in public.

He told The National: “It’s like shining a torch into a room and seeing the cockroaches running – we need to open the curtains on this.

“They gave the names of four long-dead men. They are nothing – this is over a generation ago. We want to know about the guys from the late 80s and 90s and now. The quote from MI5 puts it in black and white – children don’t matter, the harm doesn’t matter. The act of government is to care for the nation. If children don’t matter, what does? These are seriously violent, ghastly crimes and they published this just before the parliamentary recess with such reticence. It’s more like crisis management than anything else.”

He added: “We have no hope of a full public inquiry into these guys. The Tory party and the Labour Party are hopelessly compromised because they have figures involved. We will never catch all these people because they don’t want us to get justice. They treat us with utter contempt. It’s shameful.”

Calling for more support for victims of child sexual abuse, he went on: “The only way to get more arrests is to look at care for the survivors. If we look after their needs we will have more people come forward, we’ll get more witnesses, more prosecutions, we’ll remove these creatures from society.”

Prime Minister David Cameron called on anyone with information about “these terrible crimes against children” to go to the police, adding: “The police on their part should then follow the evidence without any fear and without any uncertainty about how high they can go – they can go as high as they like.”

Earlier this month, Danczuk, who investigated claims against former MP Cyril Smith, revealed he is to step back from campaigning on child abuse due to the strain on his mental health. He said collecting victims’ testimonies had led to suicidal thoughts. “I have been suffering from depression to the point where I have decided to seek help,” he said.