Single sex exemptions have been legal since the Equality Act 2010 was introduced. They were never and have never been illegal, even though trans people are also protected from discrimination.
Delighted to see the law is finally being correctly stated. There's never been any legal necessity for mixed sex facilities.
www.dailymail.co.uk/news/article-14422391/Yachtswoman-Tracy-Edwards-sailing-club-trans-member-changing-rooms.html