As the last of the prisoners clambered out of the back of the van, a voice came from an overhead speaker. This time it was male, but equally mechanical. "The outer door is about to close. Please stay well clear of the yellow line." On the wall beside the door, a red light began to flash. A buzzer beeped softly in time with it. "The door will be closing in five, four, three, two, one .. ."