Why does Hollywood love British movie villains?

Sir Ian McKellen took on the role of the villainous Magneto in the X-Men films, Paul Bettany was Silas in The Da Vinci Code and Alfred Molina played Dr Otto Octavius in Spider-Man 2.Others include Sir Ben Kingsley (Nizam in the forthcoming Prince of Persia: The Sands of Time), Sir Anthony Hopkins (Dr Hannibal Lecter), Brian Cox....