Here's what happened: Two journalists for the Daily Mirror were carrying the alleged fake bomb onto the London Underground when they were stopped by railway staff, who questioned them and eventually called police. The men were soon arrested under the British Terrorism Act, with police raiding their homes.
The journalists say they were just undertaking investigative journalism, calling the object not a bomb but a "tracking device" designed to test rail freight security.
"The aim of the police is to undermine journalists and stop them carrying out investigations of legitimate nature," the Daily Mirror head of news, Gary Jones, told the Guardian. Last year, a Mirror spokesman told the paper, "Mirror journalists attempted and succeeded in planting a fake bomb on a nuclear train, which highlighted serious security lapses. We therefore felt that it was a legitimate and justified journalistic exercise to repeat the action in the interests of public safety."
Peter Greenslade isn't so sure.
If carried out successfully, he writes, "this kind of tabloid stunt journalism" "provides a splash with a picture of an oh-so-clever reporter scampering about with a box of wires and a leading article decrying security lapses. But what does it really prove? The undeniable fact is that 'total security' is both unrealistic and, in a democracy, undesirable. It may even have the opposite effect to its journalistic intention, by demonstrating to would-be terrorists how easy it is to beat security measures."
I have to agree with Greenslade here: Even though the previous such stunt by the Mirror led to improvements in security, there are very few circumstances where a news outlet is justified in taking an action like this. Sure, it would be interesting to see what would happen if an American news organization planted a fake bomb on the New York subway system; it would likely also divert police resources, inconvenience thousands of commuters, and spark outrage at the press corps for creating news instead of simply covering it. (Not to mention, as Greenslade argues above, potentially providing a lesson for terrorists.) It's hard to see how such an undertaking would be in the best interest of anyone other than those bean counters and glory-seeking journalists who are willing to try anything to bring in a few more readers or viewers.