It seems it’s too much to ask government departments to get it right.
There are 23 ministerial departments listed on gov.uk and 20 non-ministerial departments. At the time of writing (October 2020), 17 Ministerial and 18 non-ministerial departments were advertising vacancies.
Many use the same recruitment system, but several are different.
All of them ask for the ‘gender’ of the applicant; not one asks for their sex.
Some use the terms female and male, even though those the are the correct terms for sex, but others use man and women, presumably because someone thought those were gender terms and even though they are defined in the Equality Act 2010 in relation to the protected characteristic of sex.
Others use the term ‘non-binary’ but provide no definition of it; some allow the applicant to ‘self-describe’ their ‘gender’.
None mention the Equality Act 2010 to explain why they are gathering this information. None of them list the protected characteristics or inform the applicant of their rights under the Equality Act.
Check out screenshots of the relevant sections of their equality monitoring forms: