Searching through my council's Equality, Diversity and Inclusion policy document, I have discovered that there are 3 options to choose when asked your sex: male, female and other. Which was news to me!
Others of their diversity documents include a fourth sex: non-binary. They also ask for information on sexual orientation and if "your gender assigns with your gender assigned at birth".
I'm going to write to them to point out that they're misrepresenting the law and making the error of mixing sex and gender. Is this a common thing now? My council is very proud of its Stonewall credentials (obvs).
This is what is written in their policy document about the EA:
The relevant protected characteristics are:
age
disability
gender reassignment
pregnancy and maternity
race (includes ethnic or national origins, colour or nationality)
religion or belief (or no belief)
sex (men, women, other)
sexual orientation
marriage and civil partnership (only in relation to eliminating discrimination)