The Danny Boyle-directed film was nominated under 11 categories and won seven, including the Best Director for Danny Boyle, Best Adapted Screenplay for Simon Beaufoy and Best Sound Editing for Indian sound technician Resul Pookutty at the British Academy of Film and Television Arts (BAFTA).
The underdog winner story with Indian cast and crew is a strong favourite to win awards at the Oscars on February 22, where it has been nominated under 10 categories.
"It's getting better and better and let's hope for the biggest one-the Oscars," said Rahman after winning the award, which were held at the Royal Opera House in London's Covent Garden.
Director Danny Boyle said the award was for Mumbai.
"We are hugely indebted for everybody honoured and those who were nominated tonight, to the people of Mumbai especially the actors Anil and Irrfan and all the other young actors who helped us- Ayush and Azhar," said Boyle after accepting the award for Best director.
British-Indian Dev Patel and Indian actress Frieda Pinto were also nominated for the Best Actor category and Best Supporting Actress but lost to Spanish actress Penelope Cruz and actor Mickey Rourke respectively.
But Patel did not seem disappointed. "Its a thrill for me. I feel so blessed," said Patel, who plays the protagonist 'Jamaal' in the film.
"To be honest we didn't really think about it. It was really absolutely fantastic. 'Slumdog...' has completely swept BAFTA awards and they have accepted it. Everybody is absolutely exhilarated with what is happening," said Bollywood actor Anil Kapoor, who plays game-show host Prem Kumar in the movie.
"With just the way people have responded we have already become a winner of sorts. Winning the Oscars would be the cherry on the cake," said film's co-director Loveleen Tandon.
The film was also hailed by star couple Brad Pitt and Angelina Jolie, who termed it as "lovely film".
Pitt's film, "The Curious Case of Benjamin Button" was also nominated under 11 categories at the BAFTA but managed to win only three awards in the categories—Production Design, Make Up and Hair and Special Visual Effects.
"It is nice to see such reaction in America and we are opening up to other cultures in the world," said Pitt, who lost to "The Wrestler" star Mickey Rourke in the Best Actor category at the BAFTA.
The other top winners at the star-studded ceremony were British actress Kate Winslet and late actor Heath Ledger.
Winslet, who has already bagged two Golden Globe awards, picked up the BAFTA in the Leading Actress category for her role as a former Nazi prison camp guard in "The Reader". She had previously won the BAFTA in 1995.
Australian actor Heath Ledger, who died last year due to an accidental overdose of prescribed drugs, received a posthumous BAFTA nod for Best Supporting Actor for his
villainous performance as 'the Joker' in Batman movie, "The Dark Knight". Ledger has also won an award at the Golden Globes and is a strong favourite for the Oscars as well.
Spanish actress Penelope Cruz won the Best Supporting Actress award for her role in Woody Allen's film "Vicky Cristina Barcelona".
Comedy film "In Bruges" won the award for Best Original Screenplay, while "I've Loved You So Long" was awarded the prize for Best Non-English language film. James Marsh's "Man on Wire" won the BAFTA for outstanding British film.
The British Academy of Film and Television Arts awards are considered the Oscars of Britain and are now seen as an indicator of probable winners at the Academy awards.
