When Gog is holding out the £20 note for Jez to get him a kebab, as the camera shots change it goes from unfolded to folded in half then back to unfolded and changes position between his fingers.
At the World War II reenactment, a Challenger tank is in the background behind Darryl, these weren't produced until the 1980s. Also shown in this scene is an FV603 Saracen (introduced in the 1950s) and an FV721 Fox and FV101 Scorpion, which were introduced in the 1970s.
When Mark, Jeremy and Darryl are riding in the taxi, they go up Croydon High Street then turn off onto Whitgift Street (next to the flyover), but when Jeremy says "Let's lose the cone" the taxi is back on the High Street and when it cuts back to Mark and Darryl in the back seat they're still going along Whitgift Street.