Many thanks for your tips. I will contact the citizen's advice bureau. I left the job beginning of September. I waited mid-September and when I saw no mail coming I called my boss who told me that he is also waiting for the P45 and will send me it ASAP. I called him back at the beginning of the month and he is telling me that I need to confirm him my address and my DSS number or the details of my new employer if I have one. I have been in London for less than 1 year so I don't know if he is lying to me. Anyway I try to stay positive, and hope to receive this money before Xmas...