Play School presenters went in front of the camera stoned after smoking "the biggest joint you've ever seen", according to a new BBC documentary.
BBC bigwig Sir David Attenborough even complained about the smell of drugs in the corridors of Television Centre in west London after pop groups smoked joints before performing.
Presenter Johnny Ball told a film crew that two of his co-stars filmed a nativity scene for long-running children's TV series Play School while stoned.
Speaking on a BBC4 documentary, Lights! Camera! Action! Tales of Television Centre, Ball said: "There was Rick Jones, Lionel Morton and myself. They got stoned on the biggest joint you've ever seen - in the studio. We were in silhouette as the three shepherds with our crooks. Lionel purposely held his crook so the crook didn't show.
"They were absolutely stoned out of their minds. So when we recorded, who cocked his lines up? Me."
Presenter Joan Bakewell said there were complaints about musicians who "didn't smoke ordinary cigarettes" and said Sir David - then BBC2 controller - complained about the "herbal smell" drifting down the corridor.
The show, which features interviews with dozens of BBC staff and on-screen talent including Sir Terry Wogan and Brian Blessed, also reveals Barry Norman narrowly escaped the sack after a corporation executive thought he wore a wig on screen.
Norman said: "I wasn't actually wearing a wig, I was just having a bad hair day."
The programme also lifts the lid on what went on behind the closed doors of the stars' dressing rooms, with former Doctor Who actress Katy Manning, who played Jo Grant, said: "People were bonking all over the BBC. Everybody was doing it on the premises."