The inmates in the film are all played by real ex-inmates who have served time in Thai prisons.
Joe Cole went through months of extensive boxing training and spend much time with the real Billy Moore and his family in Liverpool before shooting started.
The real Billy Moore makes an appearance in the film as his own father, who had died of cancer before filming began.
All of the fights in the movie are real. Joe Cole (Billy Moore) said his make-up artist spent more times covering up bruises and cuts than adding.
Somluck Kamsing, who plays the boxing trainer Suthin, has won the Olympic gold medal for featherweight boxing in 1996.