I've just finished watching an episode of The Memoirs of Sherlock Holmes, from 1994, and one of the characters was, I thought, a very young-looking Hugh Bonneville.
However, when the credits rolled, it appeared it was a Richard Bonneville.
Gosh, thought I, does Hugh have a brother, or a twin? So I looked up Richard Bonneville.
Haha! It appears that when Hugh Bonneville started acting, he took his middle name, Richard, and only later changed to his first name, Hugh.
Mystery solved!