This question is related to gender issues, and should be seen in that context.
A person's legal gender in UK law and on official UK documents such as a passport, is legally determined. But what about the title they stipulate on the same documents? That seems a lot more open to choice.
This question is about whether their title on such documents is of their own choosing, or whether it's legally limited in any specific ways (and if so, on what legal grounds and how it is limited). I'm assuming the title is one they use everyday.
Traditionally and usually, a person who is legally recognised as male uses "Mr" as their title, and a person who is legally recognised as female uses "Ms" or some variant on theirs. The main exception is if they have some other title they are known by, such as Dr, Lord/Lady, Professor, or any of several others. But what determines whether some title is able to be used on their official documents?
What promote the question is that the title, unlike gender, does seem to be something that a person can choose or acquire without legal recognition, and in many cases it's completely up to them the title they wish to have, and their choice will be used on official documents such as a passport, other than on the grounds of legal designation.
Three quick examples (there are probably others):
A person may have a social award (a degree or tenure for example). If so, they might still choose to be known as Mr/Ms but could at will opt to have a passport with title Dr or Professor.
If female and unmarried one person might choose Miss and another Ms.
if married one person might choose Mrs and another Ms, but presumably a married female who wished to continue using Miss as before would not have their passport application rejected. (My reason for this guess is that if they didn't change name they would not have their old passport invalidated just because it used "Miss" and was therefore legally incorrect, on the grounds they were legally now "Mrs". I could be wrong though?)
There seems to be scope/flexibility for a person to choose what title is used for them on their passport. I'm not aware of a UK law saying what title a person may or may not use. So how much choice is there? What governs valid and invalid choices of personal title?
More specifically, can one state a gender-indicative or marriage-indicative title at will? Two quick examples:
Could a legally female person who was not married but habitually used "Mrs", have "Mrs" on their passport anyhow?
(Examples of why they might wish to: They might be divorced but not wish to change title. But suppose they had never been married, or might use Mrs all the time and on documents because of perceived benefit in not appearing to be a single female, especially when travelling)
Would a legally male person who used "Ms" in everyday life be prevented by law from using "Ms" as their title on their passport?