Revealing mistake: During the scene where the military loses control of London, and their snipers are told "all targets are free", you can see heavy padding beneath Infected/civilian victims' shirts, etc, as they're shot. Presumably it's to stop them injuring themselves when they fall over, or to hold apparatus for the blood effects, but it's too bulky to be part of the characters' clothing.
Visible crew/equipment: In the scene where Doyle is talking to the helicopter pilot at the park, you can see another pilot on the left side of Doyle's head for a split second.
Visible crew/equipment: In the scene where Don is fleeing from the farmhouse he jumps into a boat, and there is a shot about 10:24 in where you can see him in the boat and the infected in the water. However you can also see someone sat in the boat with him, appearing to be holding a camera.
Plot hole: There is no way Don could have met his children at the underground station at the end of the film, with no way of knowing where they were going, and with no means of transport to get there that quickly.
Continuity mistake: When Andy gets sprayed with blood at the virus outbreak scene, when a sniper saves his life the blood splatter changes several times over the movie.
Other mistake: Towards the end of the film, as the two kids are escaping through the subway being guided through the night vision scope used by the army major, they are virtually blind and have to pick their way through dead bodies, escalators etc. This seems a bit unnecessary as the M4 rifle to which the night vision scope is attached also has a torch attached to the RIS rail. Military spec torches are extremely bright - why not just turn it on? They can't be worried about being spotted, because they are shouting at each other, not concerned with what might spot them.
Factual error: The route the children take to their house on the moped doesn't make sense - this is just to show the London landmarks.
Factual error: When Scarlet, Tammy and Andy enter the train station, there is a poster for Oyster Cards, which didn't get introduced until July 2003. This film is set 28 weeks after the occurence in 2002. There would be no need to update the train system, as London would have been in turmoil.
Continuity mistake: After Don escapes from the house at the beginning of the film, the infected are right behind him. He manages to escape in the boat but when the following shots show the river, there is no sign of any bodies or blood (despite one infected being killed by the boats propeller) or any disturbances on the surface apart from waves being caused by the boat. There is no chance that the infected could have all gotten out of the river so quick (including the dead infected body) without leaving so much as a splash.
Continuity mistake: Don attacks a man in the underground carpark and thumbs out his eyes as he did with his wife. The man gets up in the next shot perfectly OK.
Factual error: The aeroplane lands at London City Airport, although the passengers enter Gatwick Airport.
Audio problem: In the scene where Doyle, Scarlett and the kids jump into the Volvo estate to escape the gas and infected, a number of references are made to the car having a manual gearbox, i.e. "pop the clutch". Doyle puts the car into second gear and several shots of the gear lever are shown. However, when Doyle push starts the car and they drive off, listen carefully and you will hear the distinct sound of the gear change of an automatic box.
Factual error: There is a point when the boy and girl are travelling to Canary Wharf. A couple of shots before they arrive there, you see the DLR train approach a bend (There is a white building to the left). This is approaching "South Quay Plaza" station. This station is two stations past Canary Wharf.