I dont know why Sex Matters are using this line of arguement. The GRA is subject to the EA as is the new Scottish GRA. So no sex did not end in 2004. In fact the guidance in the EA highlight that saying you change sex with a GRC is a legal fiction, because the EA says there are circumstances when actual biological sex is what matters, not what is said on a piece of paper.
There are circumstances where a lawfully-established separate or single-sex service provider can prevent, limit or modify trans people’s access to the service. This is allowed under the Act. However, limiting or modifying access to, or excluding a trans person from, the separate or single-sex service of the gender in which they present might be unlawful if you cannot show such action is a proportionate means of achieving a legitimate aim. This applies whether the person has a Gender Recognition Certificate or not. https://www.equalityhumanrights.com/en/advice-and-guidance/separate-and-single-sex-service-providers-guide-equality-act-sex-and-gender
This was acknowledged by the SNP on radio 4 shortly after the vote, and was referred to in the Lady Haldane ruling.
The issue is why aren't more organisations or providers implementing the singe sex exemption and why groups who claim they are following the EA single sex provision then act as though those with a GRC are biologically the other sex.
The campaign should be about making sure that prisons and health organisations implement the single sex provision.
I'm afraid the reality is that no too many people actual think women's rights are of any importance.
The question we have had and continue to have the right to single sex provision but too many dont care to put it into practice.