Laminating stuff yourself usually doesn't pay. It's more expensive, more work, and the laminate generally doesn't adhere as well as melamine. Though if you don't have a saw blade designed for cutting melamine-covered particle board cleanly, it does allow you to apply the laminate after the pieces have been cut to size.
Unfortunately, I don't know where you'd get it in the U.K. Anyone that sells full-sized sheets of white melamine should be able to special-order black or any of the other available colors. A local full-service lumber yard is probably your best bet...