Bill Nighy once famously complained of being the only English actor who hadn't been cast in a 'Harry Potter' film. Luckily for him (and us!), he was offered the role of Minister of Magic Rufus Scrimgeour shortly after.
Though it certainly seems like every high-profile British actor from Emma Thompson to Helena Bonham Carter to Alan Rickman to Gary Oldman has appeared in the franchise at some point, there are still a significant number of seasoned Brits who haven't dabbled in the 'Harry Potter' magic. (Vanity Fair even compiled a list of 76 venerable British stars missing from the films.)
Some absences are less mysterious than others. While most thespians would kill for a spot in the films, others have said they wouldn't be caught dead in the wizarding world of 'Harry Potter.' Most notably, Tilda Swinton has publicly declared her distaste for the 'Harry Potter' films, reportedly complaining that the franchise "fetishizes boarding school for children." (Sounds like someone didn't have fun rubbing elbows with Princess Diana at the West Heath Girls' School.) Of course, most stars would not echo Swinton's sentiments. As Nighy once told Premiere magazine, "'Harry Potter' is an institution in England. It has become a national cultural treasure."