Revealing mistake: The list of intelligence agents names that Johnny Marks steals is a list of the same names repeated over and over again.
The Lesser of Two Evils - S1-E6
Factual error: The bomb in the laptop contains 6 ounces of semtex. Nowhere near enough to "blow up the street." Tom's girlfriend could have gone upstairs and been perfectly safe from the blast.
Episode #3.3 - S3-E3
Audio problem: In a conversation with Colin, Zoƫ says "What is the point of it being able to do all this stuff if we can't see the results?" The camera then cuts away from her face, she continues "We need to find out who [name I won't embarrass myself by misspelling] is talking to." This line has been dubbed in, as it is said while the actress' face is off-screen and in a completely different tone of voice. (00:35:30)
Episode #3.5 - S3-E5
Continuity mistake: Danny is on the range firing a chrome/silver Beretta pistol. The other agent on the range takes it from him, but when he is shown shooting it has changed to a black Glock. When he hands it back it has become a Beretta again.
Episode #4.1 - S4-E1
Character mistake: Ruth tells the Oxford professor that she read "Classics" at Oxford. That's a major mistake - Oxford doesn't offer "classics" as a course: it is called "Greats" (or "Lit Hum"), and is referred to as such by the students reading it. It might be one thing for an Oxford alumnus to call it "Classics" when speaking to someone not at Oxford, but they would never say it to a member of the Oxford faculty.
Episode #4.1 - S4-E1
Character mistake: Ruth requests a search of London streets with the name "Achilles" in them. A list of streets appears on a computer screen, but when one of them is selected, it is spelled "Achillies."
Episode #4.2 - S4-E2
Other mistake: There is a scene set in the basement of Thames House. It is one of the most secure buildings in the country, but has graffiti on the walls.
Episode #4.2 - S4-E2
Continuity mistake: The ladder carried by a bomber is a plain, ordinary ladder. After he puts it up against a post, it changes to an extendable one made up of three connected ladders.
Episode #4.4 - S4-E4
Character mistake: A computer screen giving details of the villain of the week contains various spelling and grammatical errors: "Embassey", "Assination" and "Assination of with".
Episode #5.2 - S5-E2
Plot hole: Collision between the two planes would have been prevented by TCAS (traffic collision avoidance system) computer systems installed on both planes. The TCAS systems automatically coordinate with each other and issue a TA (Traffic Advisory) with an audible "TRAFFIC, TRAFFIC", then if on a course that could result in a collision or near miss, issue an RA (Resolution Advisory) to their respective flight crews. Typically one plane's flight crew is audibly ordered to "DESCEND, DESCEND" by its' TCAS and the other plane will be instructed to "CLIMB, CLIMB" by its' TCAS. The flight crew is required to follow their TCAS instructions over the air traffic controller's. All commercial airliners are required to have a functioning TCAS computer. These systems were obviously not under control of the terrorists, they were conveniently ignored in the plot. (00:03:20 - 00:06:47)
Episode #6.6 - S6-E6
Continuity mistake: When the plane lands, they use stock footage of a Boeing 747 with four engines visible. All other shots are a 757 with two engines.
Episode #8.8 - S8-E8
Other mistake: Tariq has been tasked with finding hotel guests who share their surnames with American presidents. His computer screen is shown with the search in progress. The surname "Bush" appears twice (two presidents, but only one surname), and the counts for the two entries are different. In addition, the name "Truman" is misspelled as "Trueman." (00:28:15)
Episode #9.1 - S9-E1
Factual error: A shipping container has a sign on it written in French, part of which reads "Attente cinq minutes...", which is intended to mean "Wait five minutes..." "Attente" is the noun "wait", not the verb, so the sign should instead read "Attendez cinq minutes..." Another sign reads "2.5m", but this should be "2,5m" as French uses a comma as a decimal point. (00:11:20)
Episode #9.1 - S9-E1
Factual error: There is a picture of a container ship with the caption "Lat 27.09 N Lon 5.2W" These coordinates are in the Sahara desert. (00:13:55)
Episode #9.3 - S9-E3
Character mistake: Tariq says "I ran a probability logarithm." This makes no sense: it should be "a probability algorithm." (00:17:35)
Answer: They no longer exist. The Military Intelligence groups first appeared at around the time of the First World War. MI-1 was the original directorate, MI-2 dealt with the Soviet Union and Scandinavia, MI-3 with Germany and Eastern Europe, MI-4 handled aerial intelligence gathering, MI-7 dealt with propaganda, MI-8 with communication intercepts, MI-9 with covert operations, MI-10 were the technical experts, MI-11 dealt with security issues out in the field and so on and so forth. All these departments have either been shut down or subsumed into the Security Service, informally referred to by its original designation of MI-5, the Secret Intelligence Service, referred to as MI-6, or GCHQ, the Government Communications Headquarters.
Tailkinker ★