Deliberate mistake: David is shown to have an illegal weapon in his home even though gun control is quite strict in the U.K. Sadly, this is quite a common practice by returning war veterans who feel safer with a gun in the house, as they often suffer from PTSD, as David does.
Bodyguard (2018)
1 deliberate mistake in show generally - chronological order
Starring: Tom Brooke, Claire-Louise Cordwell, Stuart Bowman, Vincent Franklin
Episode #1.6 - S1-E6
Factual error: When Commander Anne Sampson appears in her body armour she wears the rank insignia only worn by the Commissioner (a crown over a pip over crossed tipstaves in a wreath) instead of that worn by her own rank of Commander (crossed tipstaves in a wreath). She has apparently been promoted four ranks.
Episode #1.6 - S1-E6
Trivia: In the park where PS Budd is surrounded by armed tactical response officers, a careful observer would notice that the brand of ear protection devices the officers are wearing are Z-TAC, an airsoft brand.