HNLondon run until at least 2018[1] and were well organised IMO. The speakers line up were mostly very interesting. And some of the recordings of the talks are still available at https://vimeo.com/hnlondon
If I'm not mistaken the organisers of HNLondon in its final years were Dmitri Grabov[2] and Stevie Buckley[3].
One recurring issue that I recall was the typical audience member trying to hijack Q&A to promote stuff - i.e. "can I ask a question?" then proceeds to make a comment and pitch their product instead. But that's not isolated to HNLondon.
PS: Big shoutout to Dmitri and Stevie for the awesome events that they put together back in the day.
[1] https://twitter.com/HNLondon/with_replies