Cheung was behind the cracking 1970s TVB police serial CID, and explosively gritty films such as Cops and Robbers (1979) and Man on the Brink (1981). That he's now overseeing the production of ICAC-backed anti-graft advocacy dramas makes his current standing even more beguiling.

However, Cheung says he's enjoying life at the ICAC. 'I was working on realist dramas at TVB anyway,' he says. 'It's the same now when I work on ICAC Investigators. We get to talk to the real case officers, and we are much closer to the truth as it happened. It's better than making the stories up myself, making assumptions of what life at the ICAC was like ... and the things I hear now are much more captivating and interesting.'

Cheung's first spell on ICAC Investigators was in the early 1990s, when he worked on episodes of two previous instalments of the now 30-year-old serial.

The ICAC has had a history of recruiting professional filmmakers to its ranks - the first series, simply entitled ICAC, was largely helmed by a young Ann Hui On-wah, and her fellow New Wave director Lau Sing-hon who has also spent time working for the commission.

In 2004, the series' directorial reins were handed over to several commercial film directors: among those joining the show on a freelance basis were Herman Yau Lai-to and Dante Lam Chiu-yin, who have since returned again for the latest series in which Cheung will also direct an episode.

Featured in the new series are stories based on real-life cases concerning insider trading, urban redevelopment, building repairs, insurance payments and the misuse of government resources.

'Our plan was to inject filmic elements into the series, and to see what kind of chemistry would result when people from the outside came in to work for us,' says Anita Lo Heung-lan, the ICAC's chief mass media officer and co-producer of ICAC Investigators 2009.

Lo (right with Cheung) says it wasn't all smooth sailing during discussions about how the latest series should proceed.

'We did have big arguments with the directors,' she says. 'It was more about how to tackle the material. Their emphasis is on the story, and they want the [anti-corruption] message to be shaped more subtly; of course. And we wanted that to be more explicit ... but they [the filmmakers] have been flexible.'

Lo says the filmmakers want their work to be for the social good and that their episodes relay the kinds of messages the commission is trying to get across.

It's a challenge for the producers and filmmakers to overcome the public perception of ICAC Investigators as a vehicle for government propaganda, says Lo. Collaborating with other external parties to lessen this perception, however, is tricky, she adds, citing an experience with the producers of the recent 1970s-set crime thriller I Corrupt All Cops. Lo says the Cops producers only inquired about a possible collaboration after finishing their film, and her team soon decided that the film was littered with too many factual errors and presented a skewed representation of how investigators actually operate, and so decided not to work with the producers.

'It can be a very thrilling film, complete with gunfights and all that, but it might not be how our colleagues work,' she says.

'We have to make sure that we strike a balance and see how we can bring out our message without resorting to extremely stirring melodrama.'

ICAC Investigators 2009 (in Cantonese) screens on TVB Jade on Saturdays, 8.30pm