Dame Helen reigns supreme at Baftas.
While The Queen won two awards, it was almost a case of mission unaccomplished for James Bond movie Casino Royale, despite being nominated for nine film awards.
A "king" also reigned when the best actor prize went to US star Forest Whitaker, 45, for his powerful role as the brutal, deranged Ugandan leader Idi Amin in The Last King of Scotland.
Whitaker beat 007 star Daniel Craig, who had hoped to become the first Bond to win a Bafta.
The Departed's Leonardo DiCaprio, Peter O'Toole in Venus and Richard Griffiths in The History Boys had also been up for best actor.
The Last King of Scotland, based on the book by Giles Foden, and shot in Uganda, won a total of three Baftas, including Outstanding British Film of the Year and Adapted Screenplay.
Dame Helen, 61, had always been favourite to land the prestigious best actress prize following a string of awards, including a Golden Globe, for her acclaimed role as the monarch in The Queen.
The story of the Royal Family in the aftermath of the death of Diana, the Princess of Wales, beat ensemble piece Babel, organised crime thriller The Departed, The Last King of Scotland and black comedy Little Miss Sunshine to best film.
Dame Helen had faced fierce competition for best actress from Dame Judi Dench, 72, for her role as a lonely but twisted history teacher in Notes on a Scandal.
But Notes on a Scandal went away empty-handed, despite being nominated for three awards.
Pan's Labyrinth, the fantasy set against the backdrop of fascist Spain, as well as The Last King of Scotland, won three Baftas each.
British director Paul Greengrass, 51, took the best director title for United 93, the docu-style retelling of the hijacking and passenger revolt on September 11, 2001, on the United Airlines Flight 93, which failed to reach the terrorists' intended target.
Dame Helen Mirren at the Bafta Awards Picture: IAN WEST; Daniel Craig