Continuity mistake: When Brant kills Barry at the end of the movie, Brant lowers his gun after shooting him, but in the next shot he is pointing his gun at Barry. Also, the scene shows Brant holding a semi-automatic style handgun before shooting Barry, then when the scene pulls out it shows him holding a revolver, then shows him holding the semi-auto again.
Plot hole: If Bradley Cooper was able to "quintuple" his money every day in the market as he claims to have done, he would have been able to earn the $100k he borrowed from a loan shark within a few days, starting from $800. Alternatively, he is shown in one scene winning a pot in poker where he could presumably also make a large amount of "seed" money from gambling. There was no need to borrow such a small sum of money from a loan shark, making the entire sub-plot unnecessary.
Other mistake: In the pre-credit scenes when the chopper spots the runaway car, Driver guns it (he clenches his jaw, fists and you hear the engine revving and gears changing) but he never catches up with the two cars only a few feet in front of him (which are proceeding at normal speed) for the whole length of the bridge.Giacomo Chizzola
Revealing mistake: While Bishop and Steve McKenna are practicing with various firearms, a slow-motion shot in the film of Steve shooting a .50 caliber rifle shows that, while the sequence depicts him firing "live" rounds, the extracted shell casing is from a "Blank" cartridge (evidenced by the crimped forward portion of the brass casing). (00:34:15)
Audio problem: This scene is repeated multiple times in the movie: usually when the main character enters the "source code" the scene begins by panning over a small pond showing a Canada goose taking flight. However the sound editor makes the mistake of dubbing in a recording of a hen mallard duck.flynn
Factual error: In the scene straight after the opening credits we are taken to Baker Street where construction work is being done. This work is identified by a sign with a logo as being for the underground line. The logo type face was developed by a Mr. Edward Johnston for London Underground from 1913 but the distinctive typeface used in the film was not in place until 1919. This is obviously long after the 1891 setting of the film.
Continuity mistake: After meeting Elise on the bus and getting his Blackberry dumped into his coffee David Norris calls his friend Charlie with his "spare phone" (silver). But after a cut or two you can see that he uses his BlackBerry again. So he has changed the phone during the conversation AND his coffee BlackBerry seems to be working again. (00:19:20 - 00:20:10)
Factual error: George Smiley stays in a hotel near Liverpool St Station, London to investigate the spy at the heart of the circus. There is one scene where we see, from above, a train leaving the station. Liverpool St station is electrified using overhead wires - the train is leaving a station using a different electrification system called 3rd rail which has never existed at Liverpool St.