you can legally use any name that is on a cerrtifird copy of an entry in a record of the registrar general. if you were born after 1972(I think it was) your surname is on your birth certificate, if born before you were not given a surname, only your mother and father (if included on the registration) have surnames included, therefore u can leaglly call yourself by either surname. After marriage you can use any name you choose from any of your registrations as long as it is not for illegal purposes and it is the name you will usually be known by. I use my maiden name and married name on the electoral roll mainly so that in future generations if they want to research their family history they will have no problem knowing they have the right ancestor. I have been doing that since 1988.