PIE was a group on a public mission to gain respectability for sexual relations with children and acceptance for the adults obsessed with child sex.

It was also a front for a depraved criminal network which abused vulnerable youngsters, often from social care.

Behind closed doors PIE was also an exchange for perverts to swap materials such as photographs and lurid sexual fantasises which fed their lust for sex with the most vulnerable youngsters.

Among its members was a top diplomat and a top official who had access to vulnerable children, and also influential people in government.

The question of the existence of links between the Paedophile Information Exchange and important public figures has potentially explosive ramifications. In 2012, Labour MP Tom Watson raised the possibility during PMQs that a paedophile ring had used to operate at the heart of power. It stunned the House into silence. A police enquiry named Operation Fernbridge continues.

One man with close establishment ties who was also involved in PIE was Peter Righton – real name Paul Pelham. He was a man who held a position of power on the National Institute of Social Work quango as its director of education. He also did consultancy work for the National children's Bureau. As well as this, he abused children for years.

Righton sexually abused youngsters with other members of the PIE network during the 1970s in London at the notorious Elm Guest House. One victim told the Mirror how he was abused by the network for five years from 1977. Righton made clear his connections with fellow public figures to the vulnerable teenager (now in his 40s), saying: "We can look after you and protect you. I have a friend who works in the government. He will be able to help."

The teenager also claimed he saw the MP Cyril Smith with Righton. Smith was exposed as a predatory paedophile following his death in 2012.

Righton did not cover up his connections to PIE and even endorsed a book by former PIE chairman Tom O'Carroll in 1990 called Paedophilia: The Radical Case. Writing on his blog, O'Carroll said: "It's still there for anyone to see."

But justice finally caught up with Righton when police raidded his home and seized copies of a paedophile magazine called Ben and a magazine called The Stud Boys. In those same raids was recovered information which sounded the alarm to his involvement in the evil paedophile network. The papers showed Righton had abused and pimped boys for years.

Righton was convicted under his real name in 1992 of importing and possessing photos of naked boys.

Another top public figure with links to PIE was the diplomat Sir Peter Hayman. A former British high commissioner to Canada who was also an top civil servant at the Foreign Office and the Ministry of Defence, Hayman's links to PIE were exposed when he left a parcel of paedophile porn on a London bus in 1978. It contained wads of diaries of explicit sexual fantasises – including killing children by sexual torture. There was also correspondence with members of PIE.

Hayman's indirect links with PIE further came to light when O'Carroll was charged with corrupting public morals in 1979. Police established that Hayman was using the alias 'Henderson' in letters to other members of PIE. Hayward was mentioned at O'Carroll's trial, again as Henderson. O'Carroll was jailed for two years. Hayward never faced trial over his membership of PIE, but his reputation was ruined. It was reported that when he was confronted with evidence of his proclivities, Hayward broke down in tears and said: "It this gets out, I'm either shooting myself or going to Brazil."

The failure to swiftly prosecute him helped fuel speculation of an official cover-up. He was belatedly jailed in 1984 for paedophile crimes.

For a spell in the 1970s, PIE acquired a veneer of quasi-legitimacy among the radical left, some of whose members went on to form the new establishment. But the reality was that PIE was a paedophile network for sick people to carry out sick fantasies. Its legacy is so toxic that today it dogs even people who had no part in its activities, such as Labour's Harriet Harman.