In general (but not always) a woman takes her husband’s surname when she gets married. When you get divorced there is no legal problem in retaining this name and there may be several reasons why you wish to do so.
For example, all of your documents including your passport, driving licence and bank accounts etc may well have been changed into that name and you may not wish to go through the hassle of changing them back.
Also if you have children they will probably have your married name and because you will not be able to change their surname without your husband’s agreement (or a Court order) then you may feel it is better for you to have the same name as they do.
However if you do feel strongly that you wish to change your surname you can do so at any time. It is in fact possible to call yourself by any surname without any official document. The problem is that to change it on official documentation you need proof.
The simplest way is to ask a Solicitor to execute a Change of Name Deed. Once witnessed this deed can be shown to all the relevant organisations and authorities and they will be able to change your name on official documentation.