In a nod to dialogue from the film, Mr. Lamb repeatedly says of his kidnapped family that he just wants them (that is, the Lambs) to stop screaming. Also, both feature climax with female protagonist going in alone without backup into kidnapper's place where captives are held in a hole in the ground.
The documentary is about this particular episode
Clips are shown
The opening sequence features Sam Tyler coming out of the box and a puppet Gene Hunt kicking a 'nonce' (sex offender).