"You're never going to get prescriptive advice from a prosecution agency such as the SFO [Serious Fraud Office] on what will be adequate and what won't," she said. "They don't want to fetter their discretion and set up too-firm guidelines or rules because each case is judged on its merits."
And some Plod would have to make a judgement. And that judgement might be called into question, or even be (gosh horror!!!) wrong.