Sky News / Reuters are claiming that the same type of explosive was used in today's bomb incidents as two weeks ago.
If, as reported, this was TATP triacetone triperoxide, then it is conceivable that it came from the same batch as two weeks ago, and that this volatile mixture of impure explosive compounds had degraded over the past two weeks, hence the misfires.
Alternatively, since it is known to be so unstable, perhaps it was stored in a wetted state for safety, and it was not dry enough to detonate properly.
No doubt the Metropolitan police will not officially release any details for some time, and there will be "anonymous intelligence sources" who are quoted by the media, possibly even foreign intelligence officials, who always seem to know more about these details than the Uk authorities bother telling the UK public.
I'm just waiting for someone - Ian Blair, The Sun, whoever - to announce that the bombers didn't have enough explosives to mount "proper" attacks because the police recovered the explosives from that car in the car park at Luton railway station, thus linking the two attacks together AND proving that the police thwarted this week's attempt.
These guys seem to reckon the terrorists were just incompetent, kinda scary but hey, Sick jokes will always float to the surface.
http://geocities.com/radio_free_london/20050721-16.mp3