The incredible tale of a once-crooked New Zealand banker who laundered millions of dollars for Mexican drug cartels is set to become a film with help from the New Zealand Film Commission.

Eric Bana has already expressed interest in the lead role.

The film, with the working title The Banker, is based on Undercover, a new book by Keith Bulfin, published by Random House, about his work for US drugs police and encounters with the some of the world's most ruthless gangsters.

Bulfin, 64, was born in the small rural town of Milton, near Dunedin, and moved to Melbourne in his early 20s, forging a high-flying career in finance until he was imprisoned for fraud in 1997.

After his release three years later, Bulfin said US agencies recruited him because of the friendship he had formed with a Mexican fugitive while in jail. Bulfin spent the next few years carrying out high-risk covert operations for the US agency.

Bulfin, who lives in Melbourne, approached the New Zealand Film Commission for help in bringing his story to the big screen.

The film commission put him in touch with New Zealand producers Showdown Film, which is now developing the film with Australian company New Holland Pictures.

The project has generated interest worldwide from Canada, Denmark, the Netherlands, US and Singapore.

When Emma Slade of Showdown Film heard Bulfin's story she flew to Melbourne to meet him. "I remember thinking this guy is either completely nuts or this is one of the most extraordinary stories I've come across," said Slade.

After several meetings and seeing letters and tape recordings relating to his work in Mexico, Slade is convinced Bulfin is telling the truth. "I absolutely know it all happened," she said.