Unfortunately we shut it down when COVID hit. I think there's a smaller, less formal HN meetup still happening occasionally but I'm not affiliated with it.

how did you go about organising this in terms of getting the word out? Did you just mention it a lot here, or via some other platforms too/instead?

We'd announce it on here and on twitter but we managed it on meetup.com so if you were a part of the HN London meetup group, you got emailed every time the next event got announced.