Have you actually suffered any loss? in what way are they damaging? i'm presuming you haven't lost your job over it. If you have hundreds of thousands of pounds with which to bring a civil case, good luck to you, as the police wont be interested in the slightest (as far as i recall it's not even a criminal offence) however, any case you might win will only compensate you for your losses (although you haven't given details, on the face of it they seem small to non-existant). You ask if you need to find out who it is - if you don't find out who it is, how are you going to mount any sort of "case" in the first place? In my honest opinion, if your boss knows these allegations aren't true, the best thing you can do is just get on with your job and do well in it.