A title is not a name#
Mr, Mrs, Ms, Miss, Mx and Dr are not part of your legal name, which is why GOV.UK's deed poll guidance says you cannot use a deed poll to change titles. There is no register of titles and no law that lists the permitted ones, so a gender-neutral title is as valid as any other. You change it the way you change any title: by telling each organisation what to use. Can a deed poll change my title? covers the general rule.
What organisations do with Mx#
Because the title lives in each organisation's own records, the answer is organisation by organisation, and the two banks that publish their policy show the range.
NatWest says it can update titles to gender-neutral titles such as Mx, and that a change of gender status on its records needs no documentary evidence, though it can currently record only male or female. Nationwide changes a title in branch or by post without any proof of ID, and reissues your card and chequebook in the new title, but says that not all of its accounts can currently be opened with a gender-neutral title such as Mx. If a system will not take Mx, the usual workaround is to leave the title blank, which most banks allow.
Passports#
A UK passport prints no title, so there is nothing to change. GOV.UK's guidance says you can include professional titles, such as doctor or professor, and honours in the "other title" box of the application with evidence, and they appear on the observations page rather than as part of your name; a title of nobility is the exception. Mx, like Mr or Ms, is not printed anywhere.
Driving licences#
DVLA's page for changing the name or gender on a licence says the process is the same for changing a title, for example from Ms to Dr, and that you do not need to send evidence unless it is a hereditary title. The licence itself shows your name rather than a title.
Doing it in one round#
If you are changing your name by deed poll at the same time, tell each organisation the new title in the same message as the new name; both are recorded together and there is no second job. Where a form has no Mx option, ask for the title to be left blank rather than accept one you do not use.
