On a lighter note, it appears that in this case all of the main explosive charges failed to detonate. It must be rather disconcerting to press the button and find you're still sitting on a tube train or bus with a ringing in your ears and a rather tattered, smoking rucksack on your lap. Perhaps we'll hear a news item along the lines of:

Abdul Ben Banger, Msc Chemistry (failed) was found in central london with his head kicked in.

BTW from the CCTV pictures of the bombers released, it looks as if this lot were more likely to be of African origin.