Revealing mistake: After Number 6 has left the Council Chamber for the first time and is heading home, a white car is seen passing by. (00:09:10)
Revealing mistake: Number 6 sets up exercise equipment in the woods and performs several athletic stunts on a bar. In close-up, he's bare handed. In long shots, however, the stunt double becomes apparent because he's wearing gloves.
Revealing mistake: The ultra-secret location of The Village is accidentally revealed when Number 6 drinks his tea. While everything in The Village is supposed to bear only its penny farthing logo, the bottom of the tea cup is emblazoned "Portmeirion Pottery." "The Prisoner" was filmed in the Welsh resort village of Portmeirion.
Revealing mistake: At the end of the episode when Number 6 and Number 2 are addressing the crowd, in the long shots facing 6 and 2 you can tell Number 2 has been replaced with a double. (00:47:51)
Answer: It's even more obvious than you think, you know who number 1 is in the very first episode. When 2 replies to the question "who is #1?" Change the way he answers from you are number one (in the monotone or accented answer to, "You are, number 6. The comma gives you the answer. #6 is #1. It's the tone of the answer.