Earlier this week, Crown prosecutor Mark Ellison told the court there was a strong possibility if the order wasn't granted, the case could be dropped against Wang Yam, 45.
Yam's defense lawyer, Geoffrey Robertson, described the Crown's threat to drop the case a "piece of forensic blackmail," the Daily Telegraph said.
Yam is charged with the June 2006 death of award-winning author Allan Chappelow, 86, who wrote several books on the playwright George Bernard Shaw.
Prosecutors said the security risk was related to material in the defense case, the BBC said.
Yam denies a role in the killing and subsequent theft of about $40,000 using Chappelow's checks, the Daily Telegraph said.
Seven national British media groups fought against the secrecy ruling. Yam's defense and the newspapers have until Thursday to decide whether to appeal the ruling, The Times of London said.
The trial is to begin Jan. 23.