Alex Renton has letters and documentation passed to him by a secret source. He tries to track down a former member of the defunct pro-paedophile group, the Paedophile Information Exchange, or PIE.

He delves into the group's origins and discovers that figures within PIE didn’t just groom the people around them, they attempted to groom whole movements.

The group formed in 1974; a time when marginalised groups were campaigning for equality and legal change. PIE took heed, that’s what they wanted.

So they aligned themselves with minority rights groups. And, these groups, whose ethos was to be open hearted, trusting - bought into it. They were fooled.

Alex Renton speaks with men who were part of gay youth groups in the 1970s that were targeted and manipulated by PIE and its members.

And he makes a breakthrough with the membership list.

Presenter: Alex Renton Producer: Caitlin Smith Executive Producers: Gail Champion and Gillian Wheelan Story Consultants: Jack Kibble-White and Kirsty Williams Sound design: Jon Nicholls Theme Tune: Jeremy Warmsley

Details of organisations offering information and support for victims of child sexual abuse are available at bbc.co.uk/actionline.