I searched for "seafarers discharge certificate uk", on my search, second result down is entitled "Guidance & Regulations and points at http://www.mcga.gov.uk/c4mca/mcga-404.htm which comes back as a Page Not Found so I went to Googles cached copy.
On there, is a link to the discharge certificate PDF.
Maybe its cos I spend too much time online 😀
Yeah still technically there! I did 6 weeks offshore during the first 6 months, I believe it taking it easy (seems to be working).