Yes, this is what I was getting at when I said that although male and female are protected characteristics, it is harder to justify having a male only association than a female one due to the legitimate aim test.
The example of welders is a good one. Welding is a very male dominated occupation. If you want to have an association for male welders and exclude female welders, it's difficult to see what the legitimate aim is. It just looks like you're excluding an already small minority based on their sex, and what is your legitimate aim? It's not difficult for male welders to find and associate with each other, and they don't need to exclude female welders in order to do that. Whereas female welders are a small minority in the profession and if they want to set up an association for female welders they can make the case that it's a support and networking group for people who are a small minority in the profession and want to discuss matters of common interest, such as, I don't know, the difficulty of getting others to take you seriously in the profession, or the lack of welding equipment designed to fit the female body.
The legislation is really very clear, and it is clearer than ever now we have the Supreme Court judgment and the EHRC guidance.
The basic starting point is that you cannot discriminate against groups of people.
The Equality Act includes exemptions which allow you to discriminate in favour of a group of people sharing one or more protected characteristics. It's important to note that this is discriminating in favour of one group rather than against another group, although in reality when there are only two groups and everyone is in either one or the other (as with men and women) it's not always easy to see the distinction.
But you don't have a blanket right to discriminate in favour of a group sharing a protected characteristic. You have to first identify the group sharing one or more characteristics (e.g. women, in the context of an association for welders), and then you have to demonstrate that having an association for that group of people is a proportionate means of achieving a legitimate aim.
There are two criteria which must both be satisfied.
- the shared characteristic(s)
- the proportionate means of achieving a legitimate aim.
(The second of these is arguably further subdivided into two criteria because something may be a legitimate aim but the exclusion of people not sharing the protected characteristic may not be a proportionate means of achieving it.)
An association for women plus trans women (excluding men who do not identify as trans women) fails on all counts.
@WhatNextCatsAsDoctors is really floundering here. It doesn't even really matter whether there is a legitimate aim or not because the legislation quite clearly requires the people concerned to share the same protected characteristic. But even if the rather bizarre interpretation to the contrary were correct - which it isn't - we are still none the wiser as to what this legitimate aim might be.
What is the purpose of an association for two distinct groups of people with nothing in common (women and trans women) which excludes a third group of people who actually have more in common with both women and trans women than either have with each other (men)?
Women have more in common with men than we do with trans women.