She has enjoyed a double Golden Globes triumph, been honoured by an Oscar nomination and last night won a prestigious Screen Actors Guild award. But despite being no stranger to the winners' podium these past few weeks, Kate Winslet was once again lost for words when she collected her prize.

Accepting the guild's best supporting female actor award for her role as a former concentration camp guard in The Reader, the star - known in the tabloids as "weeping Winslet" over the speech she gave at the Globes - was overcome with emotion and appeared to forget her speech, if she had prepared one.

"It is really an honour to be included in such a remarkable year and [to] be acknowledged by my peers in this way,” Winslet, who was dressed in a figure-hugging royal blue gown," began. "I really feel like everybody should be given a medal," she said, before adding: "I'm a little bit lost for words, I'm sorry."

Winslet was ridiculed this month for her tearful and incoherent speech after winning a best actress Globe for Revolutionary Road (her other was for The Reader). She had said that she did not expect an award after five unsuccessful nominations in the past.

“I’m sorry, I have a habit of not winning things," she said, before a tearful apology to fellow nominees Anne Hathaway, Meryl Streep, Kristin Scott Thomas and Angelina Jolie. She has promised to prepare a speech in case she collects a best actress Oscar at the Academy Awards next month for The Reader.

The Briton, 33, has come a long way since starring opposite the Honey Monster in a breakfast cereal advert. That job, when she was 11, was her professional debut, but she came from a family who were used to performing. Her parents, Roger and Sally, were actors and her grandparents ran a theatre in her home town of Reading.

After attending drama school, she got her big break at 17 when she was cast as an obsessive teenager in Heavenly Creatures. A year later, her role in the period drama Sense And Sensibility was rewarded with both a Bafta and an Oscar nomination for best supporting actress. Her role opposite Leonardo DiCaprio in Titanic garnered an Oscar best actress nomination.

Off camera, she married an assistant director, Jim Threapleton, whom she had met on the set of one of her films, and the pair had a daughter, Mia, in October 2000. They divorced in 2001 and she married Sam Mendes, the director, two years later. The couple had a son, Joe, in 2003.

Also at last night's SAG awards Slumdog Millionaire, the British film set in the Indian city of Mumbai, was given further recognition. But while the film’s director, writer and musicians have already won awards, the Slumdog cast – the young British actor Dev Patel, Bollywood star Anil Kapoor, newcomer Freida Pinto, and a host of relatively unknown Indian child actors – had gone unrecognised.

So when the actors were acknowledged by their Hollywood peers and named best ensemble cast, their surprise was obvious. Pinto and Patel stared wide-eyed in disbelief as their names were read out instead of their fellow nominees, a who’s who of Hollywood including Brad Pitt, Cate Blanchett, Sean Penn and Meryl Streep.

Leading the cast onstage to collect their SAG awards, Kapoor said: “It was already enough to be nominated. To win this is unbelievable."

He went on to thank director Danny Boyle, before dedicating the award to Slumdog’s young child stars, who remained back home in India. "They deserve this award. It is the children that have done it, not us. This is on behalf of the children," Kapoor said, as Patel and Pinto embraced with excitement.

The ensemble award for the 11 cast members was the first acting honours for Slumdog, which has dominated the awards season, collecting 10 Oscar nominations. The film is tipped to win best picture at the Academy Awards next month.

The awards are voted on by guild members, and honour acting in film and television.

Hugh Laurie won his second straight SAG award for best actor in a TV show for his portrayal of the cranky doctor in the US TV show House. The former Blackadder star joked that he was disappointed one of his fellow nominees did not win. “I actually had a hundred dollars on James Spader (of Boston Legal),” the Briton said. “This is just not my night.”

Other awards went to Meryl Streep, named best actress for her role as a nun in Doubt, and Sean Penn, awarded best actor for his portrayal of a gay rights activist in Milk.

The late Austrailan actor Heath Ledger was named best supporting actor for his chilling portrayal of the Joker in the Batman film The Dark Knight. Ledger’s award was accepted by his British co-star Gary Oldman, who said: “It is a great honour to be asked to accept this on behalf of Heath. He was an extraordinary young man with an extraordinary talent and it is wonderful that you have acknowledged that and honoured that talent tonight."

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