None of the actors playing the 3 Chinese leads were native speakers of Chinese.
Both David Yip and Anne-Simone had to learn their Cantonese lines phonetically. New York born Michael Wong, who actually lives in Hong Kong and appears frequently in local movies, spoke Cantonese with a heavy American accent.
Some 18 months before being cast in this movie, Katie Ledger and Johanna Gardiner were co-hosts on a local children's TV show called JUST WHEN YOU THOUGHT YOU KNEW EVERYTHING.
Anne-Simone, an actual martial artist, rehearsed with both director Joseph Chow and co-writer Mark Sissons the kick in the playground scene when she knocks Steve's baseball cap off the teenage hooligan's head. She did it perfectly both times. When cameras actually started rolling, she broke the young actor's nose. That's the take that was used in the final movie.
The event that triggers the story was based on an actual incident - in 1992, a British civil servant died of a heart attack while jogging on Victoria Peak. The dead jogger in the film, Stewart Wilson, is based on a couple of local business tycoons, or "taipans", that the writers had interviewed for Hong Kong television.
The younger "expats" in the story are modeled after many of the writers' colleagues who worked in the English media and who exemplify the F.I.L.T.H. syndrome i.e. "Failed In London, Try Hongkong".