I did an editing job recently and I think the 'director' is trying to stiff me on payment. It was only an amateur editing job but cash is cash. He left a external HDD with the rushes on with me which is currently at my old flat, which I have moved out of (left the HDD with friends there). Am I within my rights to withhold this as collateral? I don't think he's going to come through so I might as well get something out of it.