playbirds (1978)

aka David Sullivan's The Playbirds. The Playbird Murders.
"Pornography is the heroin of the soul and people must be protected from it."
David Sullivan manages to rope in a number of familiar faces, (including Dudley Sutton), into this crime drama; a starring vehicle for Mary Millington. She gets to show off her bad acting, and a lot more, as she plays a police officer who goes undercover in the world of porn, to find a killer.
As usual Sullivan manages to produce an unsexy, and stilted drama, that could only make money in the sexually repressed British cinema of the 70's.