The Twitter hashtag for the event is #LegalHack
The event has a wiki.
Online discussions about the event are being held in this forum.
Some online discussions are being held in a Google Plus Hangout.
The organizers have made a wiki of Open Legal Data sources.
John Sheridan of The National Archives will speak at the event on 16 September.
For more details or other resources, please see the comments to this post and the event’s Website.