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. (00:17:45)
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. (01:54:00)
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. (01:54:25 - 01:55:00)
Continuity mistake: When V captures Evey as she is escaping from Gordon Deitrich's house, he has a ninja-like mask on where you can see his eyes. However, Delia Surridge wrote in her diary that he had no eyes (due to burn damage), and the flashback she had confirmed this. (02:07:15)
Continuity mistake: As V attacks all of Creedy's men with his knives, in one shot he cuts one man's neck, and blood sprays onto the man's face, but in the next shot as the man falls, his face is clean.
Continuity mistake: When the detective places the item on his desk, to confuse the scanners in the area, at first he places it on a high pile of CDs. In the next shot the item is in a different location on the desk.
Continuity mistake: In the domino scene, in the shot where the last couple of dominoes fall, you can see that there are two dominoes still standing (the obvious one and one a little further back.) In the next shot you can see that only one is still standing.
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: When Evey is wiping V's mirror clean, she stops and they talks to V. Behind her, the amount and position of white spray left on the mirror changes a few times between shots.
Continuity mistake: Even though Evey pepper-sprays Dominic directly in the face, we never see him with red or puffy eyes at any time afterwards.
Continuity mistake: The appearance of the egg on toast that V makes for Evey changes a few times. How prominent the egg is, and how done the toast is noticeably differs a couple of times.
Continuity mistake: In the opening scene when Evey is getting dressed in her room, her hair is up. After putting on her makeup she lets it down. In the next shot it is up again, and then down again in the shot after that.
Continuity mistake: In the final fight, when V slices a man's chest twice there's no blood on his face, but in the very next shot, there is.
Continuity mistake: When Gordon is on the ground after being knocked down by the door, in one shot his left hand is above his head, but in the very next shot, his left hand is below his head.
Continuity mistake: As the people are coming out to confront the finger-man who shot the little girl one of them is carrying a shovel. This same man proceeds to swing what appears to be a pipe wrench at the finger-man's head.
Answer: Nothing is ever revealed about V's history before Larkhill so we don't know why he was there. As for the roses, in the original comic book, in order to keep him compliant during his time in captivity, V was allowed to tend a small garden while his health was monitored. It was during that time that he first grew the Scarlet Carson roses and also surreptitiously obtained the chemicals that he would use to destroy Larkhill and make his escape. Whether this can be considered consistent with the film storyline is an open question - certainly nothing in the film actively appears to contradict it.
Tailkinker ★