The Queen's pleased as Dame Helen triumphs

There was a hint that a formal invitation to tea with Her Majesty may be a step closer after a Palace spokeswoman said of Mirren's Oscar's triumph: "I'm sure that the Queen will be pleased."

Gallery: Best dressed at the Oscars

Gallery: Worst dressed at the Oscars

Gallery: The Vanity Fair Oscar Party

Gallery: Brits at the Oscars

Gallery: Winners at the Oscars

Gallery: Elton John's Oscars party

Video: Stars arrive on the red carpet

Video: Highlights from the ceremony

Video: Stars at Elton John's Oscars party

Video: Backstage reaction from the winners

Blog: Nick Curtis on the 'Oscarzzzz'

Mirren, 61, is the first British film star to land a best actress gong since Emma Thompson in 1992. She beat competition from fellow Brits Kate Winslet and Dame Judi Dench with her role in Stephen Frears's The Queen.

Mirren's victory prompted a sigh of relief from her supporters and the bookmakers who had already paid out in anticipation.

She accepted her award looking a little less than flawless. After a last-minute wardrobe malfunction she took to the stage wearing only one diamond earring. "I've got my purse in one hand and my earring in the other," she said.

In her speech, she paid a warm tribute to the Queen's "courage and consistency", adding: "Ladies and gentlemen, I give you the Queen."

She told the audience at the Kodak Theatre: "For 50 years or more Elizabeth Windsor has maintained her dignity, her sense of duty and her hairstyle. She's had her feet planted firmly on the ground, her hat on her head, her handbag on her arm and she's weathered many, many storms and I salute her courage and her consistency."

Adding to the plaudits for Mirren's performance, Prime Minister Tony Blair said: "It takes a very special actress to take on a role of this kind and to do so to universal acclaim. Helen Mirren is a very special kind of actress and her Oscar is richly deserved."

Asked if he had actually seen the movie, Mr Blair's official spokesman admitted: "No."

It was the only award, however, for The Queen, which had been shortlisted in six categories - and one of barely a handful overall for British talent, despite a record tally of 18 nominations.

Forest Whitaker landed the best actor Oscar for his performance as Ugandan dictator Idi Amin in British-made film The Last King Of Scotland.

He said of his childhood in a tough Los Angeles ghetto: "When I was a kid, the only way I saw movies was from the back seat of my family's car at the drive-in. It wasn't my reality to think I would be acting in movies - so receiving this honour tells me that it's possible."

Martin Scorsese won best director for The Departed. The crime drama starring Leonardo diCaprio and Matt Damon and co-produced by Briton Graham King won four Oscars, including best film. Having previously been nominated five times for best director, Scorsese spoke of his relief at landing an Oscar. He said: "So many people over the years have been wishing this for me. And I'm saying thank you."

A tearful Jennifer Hudson was best supporting actress for her debut performance in Dreamgirls but her co-star Eddie Murphy, tipped to win best supporting actor, lost to Alan Arkin for his role as a heroin-snorting grandfather in Little Miss Sunshine. The film also won best original screenplay beating The Queen and Babel.

In a night notable for triumphs and disasters in the wardrobe department - Nicole Kidman will take a long time to live down the giant bow she sported - the greatest stir was caused by Jack Nicholson's shaved head. He is filming The Bucket List with Morgan Freeman, about two terminally ill men who escape from a cancer ward and go on a road trip. There was disappointment for Patrick Marber, whose Notes On A Scandal had four shots at Oscar glory but failed to pull off one.

Peter O'Toole's eighth nomination, as best actor for Venus, came to nothing, and Paul Greengrass's dramatisation of the September 11 hijack, United 93, also failed to translate its two nominations into any awards.