Continuity mistake: During the scene where the government agents go to arrest Evie at the BTN, V shows up and the building is evacuated. The agents see Evie in the hallway. When Evie turns to run away from them, there are several people directly behind her in the very crowded hallway. Take note of three men, one in a dark, short-sleevd shirt, one in a long-sleeved, light grey sweater with yellow stripes and a third in a red shirt directly behind the first two, that are directly in front of Evie as she starts to run away from the camera. There is also very little room for her to run due to the crowd. When the shot changes to show her running towards the camera, the man in the sweater and the man in the red shirt have disappeared and there is a good ten feet of empty space to run in. The shot again changes to show Evie running away from the camera again and the two missing men are back and the crowd has reappeared.
Continuity mistake: In the scene at the underground station where Creedy and V are talking, after V kills the two men trying to take his mask off, and everyone backs up, it is clear that there is no one behind Creedy. However, in the next shot, when Creedy says "You won't cry like him will you?" there is a man standing behind Creedy's left shoulder. He is there until V is saying "what you have are bullets and the hope that when your guns are empty," when the angle shows Creedy and his men and, again, no one is behind Creedy.
Continuity mistake: When Detective Finch talks to the coroner about the murdered bishop and asks for her help with the rose, as he hands it to her you can see that the rose is completely covered in plastic, but when she looks closer at it, it isn't covered any more. A few seconds later when she's holding it in her hand, it's covered again.
Continuity mistake: At the scene when V and Creedy's men are fighting, when Mr. Creedy says "Now that's done with, it's time to look at your face. Take off your mask." At which point V says "No". V's cape is wide open. When the two men approach and attempt to take off the mask the cape is fully closed.
Factual error: When Mr. Creedy is firing his revolver at V after his men have been killed, the camera, positioned presumably inside the revolver behind the cylinder, shows two empty chambers out of six total, but Creedy eventually fires 5 shots. During this same sequence one of the empty chambers lines up with the barrel, but Creedy's gun somehow fires. Also, if the camera is behind the cylinder, the chambers would still have loaded cartridges or shell casings in them, they wouldn't be empty.