Behind that, a tunnel held a desk and a closed-circuit TV camera set to automatically record images of anyone passing. The mechanism also triggered a tape of dogs barking, "clearly designed to frighten people off," the spokesman said.

Further along, the tunnel opened into a vast 400 sq metre cave some 18m underground, "like an underground amphitheatre, with terraces cut into the rock and chairs".

There the police found a full-sized cinema screen, projection equipment, and tapes of a wide variety of films, including 1950s film noir classics and more recent thrillers. None of the films were banned or even offensive, the spokesman said.

A smaller cave next door had been turned into an informal restaurant and bar. "There were bottles of whisky and other spirits behind a bar, tables and chairs, a pressure-cooker for making couscous," the spokesman said.