the phrase 'sex based rights' was invented on Twitter circa 2015 - it isn't a phrase found in any legal textbook or statute. There's not, to my knowledge, reference to it in any major feminist text. It is an invention for the purposes of discriminating against trans women

There is an exemption which can be used to restrict some services to be single sex (which might in some contexts be interpreted as ones legal sex and therefore affect trans women). It is an exemption to a duty not to discriminate with a high bar. Not a right

here's evidence for the 2015 date in my original tweet} https://twitter.com/sineadactually/status/1255448405049999363