A film-maker who re-mortgaged his home to help fund his production was a triple winner at the Moet British Independent Film Awards in London.
Metro Manila, a crime thriller set in the Philippines, won the best film and production achievement prizes, and Sean Ellis was named best director.
The film is the UK entry for best foreign language film at the Oscars.
James McAvoy was named best actor for Filth and Lindsay Duncan won best actress for Le Week-End.
Julie Walters picked up an outstanding contribution award.
Brighton-born Ellis was inspired to write Metro Manila after witnessing an intense argument between two security truck drivers while he was on holiday in the Philippines in 2007.
Three years later he returned to shoot the film on a tiny budget he had raised himself.
"It's such a long journey we've had with this film with such humble beginnings," he said after picking up the top prize on Sunday night.
"I feel very honoured."
The film was shot in the Philippines with local actors and all the dialogue is in Tagalog, which Ellis does not speak.
He said one of the problems he had when looking for finance was that potential investors wanted him to make it in English, or include an American actor.
Ellis, Oscar-nominated in 2006 for his short film Cashback, told the BBC that having re-mortgaged his house to raise £250,000 to fund the film, he had now made that money back.
Picking up the award for best actor, James McAvoy said: "It's like Scotland's won the World Cup."
In Filth, he plays abusive, bigoted, drug-taking policeman Bruce Robertson.
"I'm so proud of playing this character and I'm so sad I'll never play him again," said McAvoy backstage.
He admitted that, along with Macbeth, Robertson was one of the two roles that he would miss playing the most.
He said it had been a privilege bringing novelist Irving Welsh's "abusive, beautiful, loving, nasty and hilarious weird - almost Dickensian - world onto the screen".
Winning the best actress prize, Lindsay Duncan joked: "I'm just glad I was old enough to play the part."
In Le Week-End, the 63-year-old and Jim Broadbent star as a couple in a tired marriage who revisit their honeymoon destination of Paris on their 30th anniversary.
Duncan said writer Hanif Kureishi and director Roger Michell had long been interested in older characters, but she acknowledged there had been a recent crop of films that were about older people.
"Obviously the zeitgeist is about reflecting that the people of my generation are very much alive," she said.
After picking up her Richard Harris Award for outstanding contribution, Julie Walters recalled her breakthrough film role in 1983's Educating Rita.
"Still to this day I meet women who come up in the street and say 'I left my husband because of you in that' or 'I got an education because of that film'."
Walters has more than 80 film credits to her name and is one of the most recognisable British actresses on film and TV. She is currently filming a new live action adaptation of the children's favourite, Paddington Bear.
Captain Phillips director Paul Greengrass was presented with the Variety award - which recognises an actor, director, writer or producer who has helped to focus the international spotlight on the UK.
His formidable body of work includes The Bourne Supremacy and United 93.
"There's a lot of razzmatazz around awards," Greengrass said, "but when you get an award like this and see the old clips and people say nice things it's very emotional."
He noted that British film makers were "in demand across the world".
"Independent film," he said, "is the well-spring that drives the renewal and creativity of the British film industry."
Imogen Poots was named best supporting actress for The Look of Love, which starred Steve Coogan as adult magazine publisher Paul Raymond.
Best supporting actor was won by Australian actor Ben Mendelsohn for Starred Up - the only one of the prison-set drama's eight nominations that converted into a win.
Scottish filmmaker Paul Wright was given the award for best debut director for his film For Those In Peril - a dark drama set in the aftermath of a fishing tragedy in a small Scottish village.
The screenplay award went to Steven Knight for Locke, while Edinburgh actress Chloe Pirrie won most promising newcomer for Shell.
Clio Barnard's heavily-nominated The Selfish Giant took just one award for technical achievement.
A film about jailed Russian protest group Pussy Riot won in the documentary category, while Cannes-winner Blue is the Warmest Colour won best international film.
The Raindance award went to sci-fi thriller The Machine, while Ken Loach's production company Sixteen Films and Friends were given a special jury prize.
The winners were announced at a ceremony, held at Old Billingsgate, hosted by actor James Nesbitt.