Bi+ Brixton [by Biscuit]
The Bi+ Brixton meet up, run by Libby (of Biscuit) is for bi, pan, omni, polysexual, fluid and unlabelled people and was created so bi+ people south of the river don't have to head into Central London every time they want to participate in bi social events.
This month is the boozy, pub-hosted version.
This trans-affirming meet is advertised more widely so there will be people from outside the meetup group there too, and the public.
There will be some pride flags in a cup in the middle of the table to mark the space for the meet event.
A click-and-move-around/to-view-around "VIP tour" is linked on the pub website, I haven't spotted any wheelchair accessibility issues from entrance to back yard (but do comment if any issues).
Nearest stations: Brixton Underground (also consider the mainline station next door to tube but others might be closer) - 15 minute walk / 6 min. via bus 35/37/355 from station (stop V on Acre Lane - Lambeth Town Hall stop); Clapham High Street on the South London line or Clapham North Underground Station (both approx. 10 minute walk); and a short bus ride away from Clapham Common. Many other busses also pass within a few minutes walk, e.g. 417 goes through Streatham to a couple mins. typical walk away.
The pub has a spacious-looking paved back yard (the website has a gallery), and is open til 1am on Saturday nights (food service til 10pm). The food options include burgers, and among the drinks (highlighted on website) are "Aperol spritz, cocktails and hoppy beer".
This event is monthly on a Saturday and alternates sober/boozy month to month.