One piece of evidence not presented to the jury in Rolf Harris's trial illustrates with grim eloquence, in retrospect, the prosecution notion that the veteran entertainer was a man of two distinct sides: the avuncular and trustworthy public figure, and lurking behind, the groper and abuser.In 1985 – when, the court heard, Rolf Harris was still assaulting women and was still having an occasional sexual relationship with his daughter's best friend – he fronted an educational video to warn young people about the dangers of sexual abuse. The film was Harris's idea, and he approached a director and the NSPCC for advice.

Called Kids Can Say No, the 20-minute video , shown widely in schools, used Harris's renown and rapport with young people to explain what the Australian-born star calls the difference between "yes feelings" – those prompted by properly affectionate touching such as parental hugs – and "no feelings".

"Sometimes people do things to one another that don't make them feel good," Harris explains to a group of primary school-age children before prompting them, as an exercise, to yell "Go away!" at him in unison.

In the wake of the court case, some details of the video are chilling: one filmed roleplay portrays a young girl being improperly touched by the father of her friend, an experience mirroring what the former friend of Harris's daughter, Bindi, recounted to the court.

Even people you know and trust can be abusers, Harris tells the children in the video. "You can also get a 'no' feeling from people that you do already know. It's quite hard to say no to these people because you feel that you're always supposed to be nice to them. Or at least you feel you should do what they ask you to do."

Harris had the idea for the then-pioneering film during a tour of Canada in 1982, when he saw a school theatre group tackling the subject. He phoned Jessica Skippon, a director who had previously made a water safety film with Harris, and proposed the new film, also taking expert advice from the NSPCC.

Many of Harris's victims told the court they did not tell anyone about being assaulted because they assumed no one would believe them. In Kids Can Say No, Harris tells his young audience that they should not be afraid to come forward.

"Some people don't act right with kids, and they need help," he says. "You can't protect them from trouble that they themselves have caused, and it's better to say something so that you and the family can get the help you need. You know nothing gets better by keeping quiet about it."

It ends with a tune featuring the chorus: "My body's nobody's body but mine. You've got your own body, let me have mine."

In a final sequence, with an accidental resonance that would only emerge more than 25 years later, among the singers joining in are two uniformed policemen who appear just behind Harris.