The timing seems a little too perfect for it to be just some random problem with the London PowerGrid.
Blair was due back in London (in roughly the area the 6 Explosions too place) from Scotland, in order to update and meet with his ministers ahead of Fridays talks.
I doubt this has anything to do with the Al'Qeda as was reported by once source. While the PowerGrid of late has been iffy, if you'd lived in or around London for any reasonable amount of time you'd know they don't surge, power just disapates. Only time I remember powerlines surging was when Lightning hit a transformer grid and it overloaded.
Personally I would look towards G8 Activists. After the trouble that was caused yesterday, although the thought is very scarey that they had organised themselves well enough it would explain how they got past the national security that has cause quite a number of outside attacks in the past 10years.
Still it is idle speculation until the site investigators are done.
In any case, my thoughts go out to the families of the two people who have died and the many how've been injured.
