Electrical cable

My and my missus are planning to refurbish our bathroom and wanting to install electric heated towel radiator. We have managed to find a particular one we like. It is 500 x 1600 with a total BTU 1100 or 500w, which is way more than enough for our bathroom. Could anybody tell me what thickness cable do I need to buy for this (500w) heated element? I am happy to do the donkey work and run the cable from circuit board to radiator, before I call someone competent who can connect it and sign it off. Thank you very much for answers.