How can I sell old shares? (opens in new tab)

A long time ago, when I lived in the UK, I bought a small number of shares, valued at a few hundred pounds, in a UK insurance company. They have since regularly paid a small dividend. But it's time to sell them off, if only to simplify my life a bit and make sure that things don't get more complicated for my heirs if I should die still owning them. Unfortunately I no longer have the certificates or any other proof of ownership (other than the fact that a dividend is paid into my UK bank accou...