No reason whatsoever for the UK to betray women by amending the Equality Act 2010 to allow trans-identified men into our single-sex-spaces, services and sports. Just because other countries have allowed themselves to be manipulated or browbeaten by mostly male activists into favouring trans identities over natal sex, is no reason for this country to do the same.
As for 'outing', if we are being honest in our debate, passing is very largely in the eye of the individual before a mirror, rather than in the eye of the beholder. Humans have a highly developed ability to recognise the sex of others, which has been honed by many millennia of evolution as a survival trait. There are so many clues which can't simply be disguised by clothes and hair.