how do we tell genuine transfolk from the not genuine ones?
We stick with the current law.
Under current law people can present and dress however they want with legal protection against discrimination on grounds of it - equal legal rights unaffected by gender expression.
In most situations trans people are free to do and act as the sex they identify as and present as.
However in SOME specific situations access to situations of intimacy, nudity or vulnerability can be legally restricted to those of a specific biological sex AND people with a gender recognition certificate who have a diagnosis of gender dysphoria, treatment for it, and have followed due process to legally change their sex.
No to self ID.
Obvious sidebar that this leaves things to discuss:
To reinforce that sex based exemptions are legal and necessary and prevent the lemmings over the cliff approach many groups and councils are doing in anticipation of a law change based on a questionable white paper.
To review the Gender Recognition Certificate process, to remove elements which are genuinely unfair (there are some) and make it a supportive process for genuinely transsexual people without removing the gate keeping or making it so easy that pisstakers will be able to swan through.
To look at the need for third spaces so that trans people who do not have or want to pursue GRCs are not forced to go into changing rooms, bathrooms etc where they feel unsafe.
To look generally at planning expectations for bathrooms, changing rooms, etc, at providing floor to ceiling cubicles with washbasins rather than open stalls.
But the current legal status quo does it.