Other mistake: One of the three girls swallows the wedding ring and later it's retrieved by pulling it out of her stomach, but earlier in the fight in the toilet when the boy's head came off, there were no pipes or tubes connecting the head to the stomach.
Factual error: When Gary gives the police officer his name and address as Peter Page, the postcode he tells him is invalid - in the UK, the second half of a postcode always begins with a number.
Plot hole: When they leave the B+B Gary's car The Beast is left parked outside as they walk into town. Later in the film they get to The King's Head and The Beast is parked out of the back of the pub. It's later used to escape from the next pub when it is driven through the wall. The Beast should be still at the B+B.
Continuity mistake: When in the first pub and it turns out one guy is tee-total and will only drink water, there is a shot of the glass from the inside as the pint of water is drunk down to the bottom. In the next shot, from the side of the table, the glass has some in - around 1/3 full.
Chosen answer: Strawberry Red for "Shaun of the Dead", Original Blue for "Hot Fuzz", Green Mint Choc Chip for "The World's End".
Sierra1