Balwant Chadha???, a former lecturer who has lived in Sydney for 41 years, tells an emotional story about how his mother fled the newly created Pakistan with four children after attacks by Muslim mobs in 1947.

"A lot of killing started and we were in the middle of it," he says. "There were gangs of people divided by religion - Muslim, Hindu and Sikh."

For two days the Sikh family was crammed on a train with other refugees; his baby sister died for lack of milk. The cinema is silent and Chadha is near tears as he describes his father finally tracking down the family in a refugee camp after 15 months of searching.

Just six at the time of the Partition of India, which created Pakistan as a Muslim homeland while retaining the rest of the country for Hindus and Sikhs, Chadha was later educated in Britain then emigrated to Australia despite what he calls "the white policy".

"I feel I'm a miracle boy," Chadha says. "The Australian government has been very kind - and the people."

That personal connection encouraged his filmmaking niece, who sits beside him at that Q&A, to tackle a film about Lord Louis Mountbatten's ill-fated term as the last British viceroy in India.

Charged with overseeing a peaceful transition to Indian independence, he was stymied by prime minister Winston Churchill's secret plan to divide the country to protect Britain's oil interests in the Persian Gulf and block the Soviet Union's expansionist ambitions.

Hugh Bonneville??? plays Mountbatten with Gillian Anderson as his spirited wife, Lady Edwina???, while Manish Dayal??? and Huma Qureshi??? play young lovers working in the Viceroy's House - Hindu valet Jeet Kumar and Muslim translator Aalia Noor??? - who are separated when violence breaks out.

"This story has been with me all life really," Gurinder Chadha says. "I grew up in London and, as a child, I never had a homeland as such. My ancestral homeland had become this new country, Pakistan.

"My family were all very affected by it but people didn't really want to talk about. The history that I had been taught was the British wanted to hand India back but we started fighting with each other so Mountbatten had no option but to divide the country. So all this tragedy, the Partition, was our fault."

Chadha's views began to change when she went to Pakistan for the first time, visiting her grandfather's former house, to shoot an episode of Who Do You Think You Are? in 2005. She was overwhelmed by the emotional reception from the locals and by seeing refugees from the other side of the 1947 violence living in the house.

"It was at that moment that I understood the reality of partition and wanted to do something about things that affected the ordinary people," she says.

Chadha started developing "an Upstairs Downstairs story" based on the 1975 book Freedom At Midnight, written by journalists Larry Collins and Dominique Lapierre, considered a seminal account of the last year of the British Raj. But two years into writing the script, she met Prince Charles at a reception at St James Palace.

"I said to him, 'I'm making a film about your uncle'," she says. "He immediately got very interested and said, 'What's the story? What are you basing it on?'

"I told him Freedom at Midnight, which was based on interviews with his uncle, and he said, 'You should look at these other texts as well'. One of the books he mentioned was The Shadow Of The Great Game: The Untold Story of India's Partition. I found it and that's when I got my twist."

That book revealed Churchill's plan, detailed in a secret report, to divide India before Mountbatten arrived.

"This report basically said Britain was bankrupt after the war," Chadha says. "It couldn't afford to keep India. It couldn't afford to maintain a police force and an army there. Plus there was too much agitation because Gandhi, with his Quit India Movement, was winning."

While Britain would still hand back the country, the report suggested annexing part of India, around the port of Karachi, as a military and strategic base to deter Stalin's ambitions.

"One would think that they should just negotiate that with Nehru and Gandhi, the leaders of India at the time, but Churchill had an intense dislike of Gandhi and Nehru was quite close to Russia culturally," Chadha says.

Partition was a violent, tumultuous time.

"It was the largest forced migration in human history - 14 million people were displaced," Chadha says. "We say a million people died. Other people say two million people died. One doesn't really know.

"The violence is often portrayed as people just turning mad and killing each other. But the evidence we found was that a lot of it was orchestrated. By creating a state of emergency, it meant that these changes to borders could happen very quickly.

"So you had militia groups operating on both sides. In the army, people were deserting and keeping their weapons. And it became a land grab.

"But the biggest tragedy for me was the women. Rape became a weapon, so you had fathers and brothers on all sides killing their daughters and their sisters rather than having them raped and killed by the other side. So there were terrible stories of women jumping into wells to kill themselves rather than be raped."

Chadha hopes her film - she calls it the first British film about partition since Gandhi 35 years ago - is a reminder of a political issue that remains relevant.

"We have to understand how politicians will always use tactics to divide us," she says. "Because it's easier to rule us if we're divided."

Fifteen years on, Chadha still finds the success of Bend It Like Beckham resonates.

"In all corners of the world, people come up to me and talk very fondly about something that had a big impact on their lives," she says. "Often it's young women who are now sharing it with their daughters. It's amazing that a simple story, which is really based on me and my dad growing up in London, can touch so many people."

Viceroy's House opens on May 18.

THE RISE OF GURINDER CHADHA

BHAJI ON THE BEACH (1993)

Comedy about a group of British-Indian women on a day trip to Blackpool, with a little-known cast headed by Indian actress Shaheen Khan.

Sarita Khajuria and Mo Sesay in Bhaji On The Beach.

WHAT'S COOKING (2000)

Comic drama, starring Mercedes Ruehl???, Kyra Sedgwick and Joan Chen, about four families from different ethnic backgrounds who meet for Thanksgiving dinner.

BEND IT LIKE BECKHAM (2002)

Worldwide hit comedy about an Indian-English teenager (Parminder Nagra???) who wants to play football against her family's objections. Fifteen years on, its success still resonates.

"In all corners of the world, people come up to me and talk very fondly about it," Chadha says. "Often it's young women who are now sharing it with their daughters. It's amazing that a simple story, which is really based on me and my dad growing up in London, can touch so many people."

Parminder Nagra in Bend It Like Beckham.

BRIDE AND PREJUDICE (2004)

Lively Bollywood version of Pride and Prejudice, starring Aishwarya Rai and Martin Henderson.

ANGUS, THONGS AND PERFECT SNOGGING (2008)

A fourteen-year-old girl (Georgia Groome) tries to find a boyfriend in a coming-of-age film based on two teenage novels by Louise Rennison???.

Aaron Taylor-Johnson and Georgia Groome in Angus, Thongs and Perfect Snogging.

IT'S A WONDERFUL AFTERLIFE (2010)

Little-seen comedy about an Indian widow (Shabana Azmi) who, wanting to marry off her only daughter (Goldy Notay???), murders failed suitors.