There is no way to answer this without it being ridiculous so I'm going to have a try.
I reckon you'll need to provide the following type of evidence:
(All the following receipts should be dated within the last three months)
Receipt from nailbar for set of gels
Receipt from a 'Ladies' hairdresser for cut, colour and blow-dry
Receipt from Eyebrow bar for eyebrow threading/shaping
Receipt from Boots/Superdrug for products such as strawberry & vanilla bubble bath, glittery bath bomb, nail varnish, make-up, tissues (for all the crying you'll do)
Receipt from Claire's Accessories for headbands, bangles, earrings, lipgloss
Proof of ownership or borrowing of any Maeve Binchy, Sophie Kinsella or other 'female' books from an 'approved' list
Proof of multiple purchases of lingerie, M&S knickers, stockings, high-heeled footwear and foundation garments
Birthday/Christmas cards addressed to your new female name by verifiable acquaintances
Not an exhaustive list as I'm sure there are other things that can prove 'womanly' credentials for 'living as a woman'.
For trans men:
Ownership of a dicky bow/tie and/or braces, plaid shirt, Lynx
Evidence of ability to man-spread and perfect a quizzical/concentrating serious face while rubbing your chin.
Receipt for the ownership of weights and/or membership of a gym
Receipt for boxer shorts, men's socks
Receipt for the purchase of hair trimmer for buzz cuts or receipt from local barber
Honestly - what is this evidence going to be?? It surely can't just be down to changing the name on a gas bill? Who is going to review this evidence in a way that won't 'traumatise' a prospective applicant. Admin, as we know, is a terrible obstacle.