Arse. I thought Facebook would show the event description without needing to log in. It says:
🌙 The ride is on the Bank Holiday weekend and close to a full moon. No entry fees, no tickets, no closed roads, but hopefully an enjoyable ride.
🕙 We will leave the South Bank about 2200/2230 and head out of London into the Kent lanes, arriving on the beach about breakfast time. Riders will need to be fairly self-sufficient but there is a useful halfway stop in the form of the M2 services. Trains can get you back to London from Margate.
🔀 Indicative route:
https://www.strava.com/routes/11385225