Factual error: (At 56:26) XXXX is dropped off by Eddie Temple. As you'll notice the car drives straight off (at 56:31). This not is possible as the road that XXXX lives at 7 Queens Gate Mews, Kensington is a cul-de-sac (no through road). The car would not have been able to go anywhere.
Factual error: The scene at the start of the film shows XXXX and his assistant making drugs. In the voice-over, XXXX mentions that his assistant has a double first in industrial chemistry from Cambridge, and is doing this job to pay off his student debt. This is wrong on a number of levels. First of all, there is no such subject as industrial chemistry to study at Cambridge, nor has there ever been such a subject. Only Chemistry is taught. Secondly, Chemistry is a single honours subject: you would only get at best a first in it, not a double first. "Double first" means you scored top marks in two separate subjects you study - for example if you read French and Spanish together, that would be double honours. This is not the case however for chemistry. Lastly, the statement about paying off student debt makes no sense given the film was set in Britain. At the time, student fees were no more than £3000 a year ($3800) so in a four year course you would end up paying only £12000 ($15200), plus living expenses. But loans are only repaid once you're earning above a certain limit, and then proportionally to your income - they're not "due" like a standard loan. It therefore makes no sense for the assistant to be working such a dangerous and illegal job if all he wishes to do is pay off his student debt - he has evidently worked with XXXX for a long time given how much XXXX trusts him.
Continuity mistake: SPOILER: The pistol featured on the movie cover is not the identical gun used during Gene's flashback. Although it's said to be the same murder weapon, both guns can be set apart when Gene opens his hidden cache of weapons. One gun has a noticeably blue handle.