To members of PIE the group was place for men to share their sexual feelings for children with fellow members. To mothers who pelted its activists with rotten fruit at a public meeting, PIE was a menace to children. To a young Patricia Hewitt, PIE was "campaigning/counselling group for adults" which a disgusted public had "misunderstood."

This is the reason why Labour grandees including Hewitt, deputy leader Harriet Harman and her husband MP Jack Dromey, have been facing awkward questions from their radical past.

The Paedophile Information Exchange (PIE) came in to the orbit of some of today's top Labour politicians via the National Campaign for Civil Liberties (NCCL) in the mid-1970s. The group for child sex enthusiasts affiliated with NCCL a year after it was founded, chaired by Keith Hose, in 1975.

Hose was a major force in getting PIE publicity and in its growth. Doing this meant the group described themselves as "child lovers" not child abusers and also claimed youngsters were "repressed" by the system. In this way, PIE was able to join in the febrile sexual politics debate of the period, by exploiting terms and concepts usually associated with causes such as feminism and rights for homosexuals.

PIE's agenda was altogether more sinister, although its supporters appear to have been genuinely baffled at the horror they engendered. Among the group's demands was the insistence that sex with children be legal from the age of four. Its tentacles spread far and wide in spite of widespread opprobrium. Members of PIE came from all walks of life, including at least one Anglican priest and an Establishment grandee, former high commissioner to Canada Peter Hayward.

But for anyone who was in any way politically active at the time, the existence of PIE was well known, although it was very careful to hide its full agenda. It was, in many ways, an entryist organisation attempting to gain respectability by attaching itself to legitimate groups.

Members kept in touch via a strong network which was served by the PIE's official journal 'Magpie' and also bulletins. Members used these to seek out like-minded paedophiles by stating their preferences. One apparently genuine advert was from a priest. It read: "Anglican Priest, south London, anxious to meet other paeds for friendship and help."

PIE also sold booklets with tites such as 'Towards a better perspective for Boy-lovers' and 'Paedophilia – Some Questions and Answers,' which was sent to 180 newspapers across Britain.

But the quest for respectability and acceptance met predictable animosity: in 1975 angry mothers pelted members with rotten fruit and veg at PIE's first ever open meeting at Conway Hall in central London. But invitations for PIE to speak publicly continued to flow, including from Liverpool and Oxford universities in 1978. However, the then PIE leader Tom O'Carroll's visits to both events had to cancelled in the face of opposition from the community.

NCCL stopped short of backing PIE's call for lowering the age of consent to four-years-old, but did stand with paedophiles who faced violence like at Conway Hall. At NCCL's 1978 AGM, a motion was issue which read: "This AGM condemns the physical and other attacks on those who have discussed or attempted to discuss paedophilia, and reaffirms the NCCL's condemnation of harassment and unlawful attacks on such persons," as reported in Magpie Issue 11.

Hewitt published her defence of PIE in NCCL's annual report in 1975, claiming members had been attacked in thehe Press and revealing the NCCL had complained to the Press Council on behalf of PIE. But by 1983, the NCCL's stance was very different and the group was cut loose. The NCCL later became Liberty and its current director , Shami Chakrabarti apologised for the old alligence, saying: "it is a source of continuing disgust and horror that even the NCCL had to expel paedophiles from its ranks in 1983 after infiltration at some point in the Seventies".

Rumours of more links between PIE and people in the corridors of power abounded in the wake of the Jimmy Savile scandal and stupefaction at how the devious TV personality and DJ had been able to get away with abusing youngsters for decades. It fuelled speculation of the existence of a shadowy clique of key influencers who protected each other.

In 2012, Labour MP Tom Watson raised the possibility of the existence of a paedophile ring at the centre of power in the House of Commons. His question at PMQs focused on an investigation which centred on Peter Righton, a notorious paedophile who died in 2007. He was an early member of PIE and also had top jobs at quangos, including the National Institute for Social Work and the National Children's Bureau.

Writing on his blog, O'Carroll revealed his dealings with Righton. He said: "I knew Peter Righton, though. He used to be Director of Education at the National Institute of Social Work. The man I knew was a cultured, easy-going, affable type, large and jolly. He very kindly read a proof copy of my then forthcoming book Paedophilia: The Radical Case and gave an endorsement comment for the dust-jacket, under his own name, and with his job-title included. It's still there for anyone to see."

By the time PIE was abolished in 1984, members of the group had racked up a string of convictions for homosexual acts with underage boys. O'Carroll has a conviction for distributing indecent photographs. A series of arrest of senior members by the Metropolitan Police on child pornography charges killed off PIE. But its toxic legacy to live on, as the current Labour leadership are discovering.