My reply was in response to doveholidays1703 query. She is about to get married and asked whether she HAD to change her surname in her passport as she had not long renewed it. Whether to change or not will always be a personal decision but in her situation there is no legal need for her to do so until her passport needs renewing so long as she always books any holiday under the same name as the one in her passport as as long as she takes along a copy of her marriage certificate for any situation where she needs to prove her identity but might be using her husband's surname.
As long as we all have the paper trail to prove that we are the person any document applies to we can call ourselves what we want. the conventions on this are changing all the time. In the past most married women even lost the use of the own first name in formal situations. They became Mrs John Smith and strict traditional etiquette says that only widowed or divroced women should use the title Mrs with their own first name. Of course these days we can't and genrally don't automatically assume that Mts Jane Smith once had a husband but doesn't any longer. These things are a matter of social convention not legal requirement and in the increasingly diverse society that we now are in the UK many women don't follow this convention.
For example, Quakers tend not to do so now or in the past, mainly because they never used titles so Quaker married women never called themselves Mrs and continued to be known by their own name on marriage. So much so that the wife of the founder of the Religious Society of Friends never took the name Mrs George Fox but continued to be known as Margaret Fell, Fell being the surname she had long used as her first husband's widow. Likewise many Moslem women don't take their husbands surname on marriage and whilst many adopt their husbands' name in this country for the convenience of not having to explain why their children have a different surname to them, many don't bother to change it on passports or bank accounts etc.
I am an academic and would never dream of changing my name and neither would many of my colleagues because it's important that we continue to use the name we first started publishing under. The trend for later marriage means that women academics have already established their reputations under their father's surname before they marry and to change your name mid-career could be disastrous these days. I have one colleague who has kept her passport in her 'maiden' name, publishes for work as 'Maiden-Married' and has her kids registered under her husband's name on their birth certificates but used her 'maiden' name on said certificate even though she is married to their father because that is the convention where she was brought up.
There are myriad combinations of what names we can take and choose to be known as and as long as we have the paper trail and can always prove that we are who we say we are there is no legal need to go through the rigamarole of changing everything on marriage but I do know one man who decided to do this to show just how much he loved his new wife, though it might have had more to do with the awful name his father had saddled him with at birth under the old conventions and he was more than glad of the excuse to ditch it :-) I also know another who took the name Ben Pink Dandelion to make a political point at a particular stage in his life but that's another story :-)
SM