Worried about what to say? Bring your personal worries about transphobia being signed into law, and trans friends being excluded from public spaces. You are a living person who deserves dignity. Remind your MP of that. You will also get guidance and brochures from Trans Solidarity Alliance that outlines our demands. This is mine from last year.

Money issues? Trans Solidarity Alliance provides a travel bursary that you can sign up for via the link.

Got a refusal or no response from your MP?  Come anyway! You can request a same-day appointment with your MP through a process called greencarding. They will come and see you if they’re already in Parliament. Even if they don’t, they’re made acutely aware of your cause because you showed up in person. This is my greencard from last year.

Here is the EHRC Code of Practice in full. It's a tough read, but some highlights are:

Organisations can’t provide trans-inclusive, single-sex services, or they risk being sued for discrimination. e.g. domestic violence support for women including trans women, men’s rugby group including trans men (12.68).

Trans people will have nowhere safe to pee. If you’re a trans man, businesses can't allow you to pee in the men's, and you can also be ejected from women’s bathrooms if you’re perceived as a man. Vice versa for trans women. EHRC suggests a ‘third space’ bathroom, which is discriminatory and unworkable for most businesses. (13.130-133)

Sports organisations must exclude trans people from single-sex competitions (13.73).  A women’s only sports competition must exclude trans women because of their biological advantage or face potential lawsuits (13.74), but a trans man who has undergone testosterone treatment can also be excluded based on fairness rules (13.81).

Trans women are stripped of the legal definition of ‘lesbian’, and therefore no longer have legal protections if they’re discriminated against on the basis of sexual orientation. (2.50, 2.92).

Here is the Good Law Project's better explanation of the EHRC Code.