I do wonder what would happen if I used a tile that was not used in the UK.
If you set your title to "Graf" in the passport form:
> By Royal Warrant of 27 April 1932, the use in England and Wales of foreign titles of nobility was discontinued.
> You must include the observation: THE HOLDER IS ALSO KNOWN AS (foreign title).
If you instead set your given name to "Graf", these instructions would not apply, as you are not claiming it's your title. Nor would it be evident to the passport office or any other English speaker that your given name implied a title, so provided your supporting documents corroborate that "Graf" is your given name, they'd issue a passport in that name.
However, if you used not "Graf", but a title recognised in the English language:
> A person may call themselves any name they want, as long as it is not for fraudulent purposes
> You may receive an application supported by documents (for example, a birth certificate or a change of name deed) that shows a customer is using a name that includes a description of a title (for example, Lord, Princess, Earl or Baron as a forename).
> You must include the observation: THE REFERENCE TO (description of title) IS TO THE HOLDER’S NAME AND NOT TO THE HOLDER’S TITLE.
https://www.gov.uk/government/publications/titles-included-i...
My personal favourite is if you change your first name to “Sir” and you are not actually a “Knight”, then you get the note “THE REFERENCE TO SIR IS TO THE HOLDER’S NAME AND NOT TO THE HOLDER’S TITLE” printed in your passport.
Context: I wanted “Dr.” to be added to my passport.