Advice for couples who don't want to get married
If as a couple you do not want to get married (or enter into a civil partnership), it is entirely within your rights for one or both of you to change your surname to match your partner's, giving the appearance of a married couple. It is not against the law to deceive other people about your marital status, provided that it is not with the intention of committing fraud. If you want to change your name in this way, see the section on changing your name for more details.
Note that changing your surname in this way has no effect on your marital status, and you will not gain any legal rights as a couple by doing so.
If you only want to change your title, for example to Mrs or Ms, you do not need a deed poll. See the section on how to change your title for more details.