During Saturday afternoon, 4th April 2009, on the 2012 Olympics site, a large number of high capacity BT core network circuits/cables were damaged by a Third Party. These cables were in a tunnel 32m below ground surface.
Since Saturday afternoon, BT engineers have been on site working to restore service to customers affected by this incident.
Internet circuits have not been affected
EDIT: I stand corrected, looks like a lot of internet circuits are affected, was a lot of misinformation being fed out when I first heard about all this.