Where's my shotgun?

You may have heard of Dead Rising, a video game that revolves around, if you hadn't guessed from the title, killing zombies. It's pretty violent, which has lead to some controversy, including being denied a rating in Germany. But not in the UK, they've decided to give it an 18 rating. This isn't all really that interesting, what gets me is the BBFC's reasoning: "There is no clear evidence that playing games leads to copycat behaviour." (Notice it's spelled Britishly) Is this really a worry in the UK? Are there lots of zombies around that people don't want killed? And should we be worried about British zombies making it to our shores? I may need to go get a shotgun... and a chainsaw.