Miles,
In reality, there is rarely such thing as 'anonymous reporting' for the simple fact that the reported person probably knows who did the reporting - and they can/will then undermine the reportee's position with their employers. As I suggest, a direct and open approach leading to a win-win situation is possibly the reporter's best bet. Failing that, I agree that reporting the perpetrator is the reportees only recourse because saying nothing is not an option - esp in this case. If reporting is necessary - have the door to escape tunnel well and truly open!
flipster