Hi Nick, as Alan says you can try Maplins qand other places, but please don't buy the cheapest lead that you come across. You get what you pay for with cables etc., and the cheap leads tend to have extremely thin and the minimum of screening - the braided metal that is just under the outer skin of the lead. Also the dearer leads tend to have more strands in each of the signal/power carrying wires, which makes them far more flexible and durable. The round "thingumebob" is a ferrite interference suppressor. Expect to pay £12 - 15 for a good quality lead. HTH CGJon