Considering when this film was released—during the peak of the Cold War alongside some rather imaginative science fiction and a dose of state-funded anxiety—it’s probably best viewed with that context in mind. Like many of his roles from the 1960s, Oliver Reed portrays a magnetic figure leading a group of troublemakers, and this film doesn't deviate much from that pattern. When "Joan" (Shirley Anne Field) encounters wealthy American yachtsman "Simon" (Macdonald Carey) at a seaside clocktower, he initially believes she’s working the streets. However, it turns out he’s mistaken; she is bait, and he falls victim to a violent mugging by Reed's gang—he plays her overly protective brother, “King.” The following day, Joan meets the injured man on his boat, and they narrowly avoid being recaptured by King’s group by setting sail. They find temporary safety in an isolated house but are quickly located, and during another escape attempt, they unexpectedly discover a gathering of children. Everyone is exceptionally well-mannered and pleasant—all wearing identical dressing gowns—but visibly chilled. “King” locates them as well, and he too is rescued by the children—what’s happening here? The kids insist that they are aboard a spaceship, receiving daily communications from their "teacher" (Alexander Knox) through television, and that every action of theirs is being observed remotely. As the adults try to uncover what's really going on, government agencies begin investigating. It makes for an interesting watch, though the acting feels rather unremarkable. The film sparks curiosity—to what extent could it actually be true? Is there a possibility that children are being exploited for military purposes? There’s some appealing scenery of the coast, and Losey maintains engagement until the very end, even after a slow beginning.

Source on TMDB