Meetings are every other Monday evening.
The London 3D printer users group brings together users and builders of open source 3D printers. It also provides an introduce the subject to the curious. You don't need to be a member of the London Hackspace to come to a meeting.
Meetings are every other Monday. There's more information on Meetup.
Twitter: Hashtag #London3D.
Directions: See Getting to the London Hackspace.