Continuity mistake: At the beginning we see Jim walking across the Westminster bridge towards the Parliament Buildings. Big Ben shows that it is around 8:10. Then the camera moves way back to a wide shot of the bridge, and we see that (according to Big Ben) it is suddenly 25 minutes later.
Continuity mistake: When "Mr Bridges" attacks Jim at Jim's parents home, after Mark kills "Mr Bridges" look at his left arm. (He's wearing a watch on the left wrist.) There is not a single bit of blood and no bite wound. A few shots later, there is lots of blood and a very large bite wound.
Continuity mistake: There is a scene early in the film where the garage explodes. A view from high up shows the explosion. Later in the film when Jim and Frank are on the rooftop, you get practically the same view but look at the area where the explosion was earlier. Everything is perfectly normal and there is NO sign of any explosion.
Continuity mistake: When Jim is wandering the deserted streets after waking up from his coma, there is one overhead shot of Jim walking down the street, towards a silver car. When it then cuts to a closer shot a red double decker bus appears underneath the "Landmark Advertising" billboard. A small white van/truck has appeared in front of a medium-sized white lorry, and the position of the silver car parked in the centre of the traffic lights grid changes between subsequent shots. Also between these and following shots, the position of the trash littering the streets differs.