Thinking about the London bombings yesterday, I keep coming to the same conclusion, all four bombs were planted by a single individual. I know cell phones don't work in the tube so a timing device had to be used and I believe that he simply ran out of time blowing himself up on the bus.
This is how I think this went down. A co-conspirator gave the bomber four explosive devices weighing less than 10 pounds each. The bomber was told that the bombs had timers set to go off in a series and told to place them in subway cars. The bomber then got on the Circle line and starts placing bombs. Sometime between first and fourth explosion the Circle line stops running. This is supposedly not terribly unusual. The bomber then gets on the #30 bus to find another location to plant the last bomb, but runs out of time and the bus blows up.
Does this sound possible to you, because London's Police Commissioner says it isn't .
Oh, and a scramjet may be involved. (very inside joke)
UPDATE: A new more accurate timeline put out by the London police pretty much kills this argument