Other mistake: When No.8 has been caught by "Rover" in the sea, she is pulled back unconscious to land by one large Rover and 2 smaller Rovers (one on each arm). Her legs are seen to kick (swimming style) to help them move. (00:17:25)
Other mistake: They search for the location of the Village by using map co-ordinates, which are checked out using a military aircraft. The Village is eventually discovered and found to be on an island somewhere in the Mediterranean sea. Number 6 is ejected from the aircraft back to the Village. However, in the final episode, i.e. 'Fall Out,' the Village is found to be in somewhere in the UK. They escape in a truck and end up traveling to London.
The Girl Who Was Death - S1-E15
Other mistake: When the girl makes her getaway in the helicopter and Number 6 emerges from the bushes and climbs aboard, look at the trees on the horizon as the helicopter takes off and supposedly lands later in another location. You can see that the helicopter takes off and lands in the same field. Also, the shot of Number 6 hiding behind bushes before jumping on the helicopter, and after climbing off it is the same one. It's from a slightly different angle the second time, but it's the same bush.
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.