well it seems that a security agency was running a simulated attack on the mass transit system in london,at the precise times and places the real attacks happened.as i recall norad was called offline on the moringof september 11, so that "mock" terrorist attacks could commence without interuption.
heres the link to the page with the article on londons training excercise.
http://www.boingboing.net/2005/07/10/london_bombings_coin.html