Mirren, nominated for her role in "The Queen," lost to Katie Dickie for "Red Road." "The Queen," directed by Stephen Frears, missed out in five categories, but did win the award for best screenplay, the BBC said.
Dickie's "Red Road" co-star Tony Curran was named best actor.
"This Is England," about a group of skinheads, won best independent film, while actor Jim Broadbent was honored with an outstanding contribution award. Thomas Turgoose, the 12-year-old making his screen debut in "This Is England," won the most promising newcomer award.
Director Ken Loach, whose most recent film was "The Wind That Shakes The Barley," received the special jury prize.
The "Last King of Scotland" about Ugandan dictator Idi Amin, won two awards -- Kevin Macdonald for for best director and technical achievement.
"The Road to Guantanamo," the story of three British Muslims held at the detention camp for two years then released without charge, earned the best documentary award.