"Gender reassignment" in the Act doesn't actually mean physically , or even socially. I think it even covers intention. Like, just a decision to reassign you gender to another, no action required.
"The Equality Act 2010 says that you must not be discriminated against because you are transsexual, when your gender identity is different from the gender assigned to you when you were born. For example:
a person who was born female decides to spend the rest of his life as a man
In the Equality Act it is known as gender reassignment. All transsexual people share the common characteristic of gender reassignment.
To be protected from gender reassignment discrimination, you do not need to have undergone any specific treatment or surgery to change from your birth sex to your preferred gender. This is because changing your physiological or other gender attributes is a personal process rather than a medical one.
You can be at any stage in the transition process – from proposing to reassign your gender, to undergoing a process to reassign your gender, or having completed it.
The Equality Act says that you must not be discriminated against because:
of your gender reassignment as a transsexual. You may prefer the description transgender person or trans male or female. A wide range of people are included in the terms ‘trans’ or ‘transgender’ but you are not protected as transgender unless you propose to change your gender or have done so. For example, a group of men on a stag do who put on fancy dress as women are turned away from a restaurant. They are not transsexual so not protected from discrimination
someone thinks you are transsexual, for example because you occasionally cross-dress or are gender variant (this is known as discrimination by perception)
you are connected to a transsexual person, or someone wrongly thought to be transsexual (this is known as discrimination by association)"
Interestingly, apparently intersex people are not protected from the Equality Act at all.
"Intersex people (the term used to describe a variety of conditions in which a person is born with a reproductive or sexual anatomy that doesn't fit the typical definitions of female or male) are not explicitly protected from discrimination by the Equality Act, but you must not be discriminated against because of your gender or perceived gender. For example:
if a woman with an intersex condition is refused entry to a women-only swimming pool because the attendants think her to be a man, this could be sex discrimination or disability discrimination"