As far as I am concerned they could have no earth. The DNO left them with no earth, that is their problem and liability. It is for you to be on top of them and make sure they do the right thing. Your must understand that as
@westward10 said, if the compression of the clamp causes a short it can be fatal to you and is in no way acceptable morally or legally to do that. I have had this before and got them back the same day with the right kit and do the job properly. Don't let them brush you off. If I were you I would take that clamp off in fact, but then I would never put it on in the first place I'd be too scared to. Don't mean to be mean to you, but I feel quite strongly on this subject and feel it is important to say what I said, no offence meant.