A station closure, therefore, or an instance of track blockage would result in multiple trains stacking up between stations. If those trains were then forced to evacuate their passengers, the evacuees faced walks of varying lengths through the tunnels until they could reach appropriate access back to street level. With most of the tunnels one hundred feet or more beneath street level, it made for quite a trek.

In and of itself not life-threatening, but certainly an added complication for riders and rescue teams, should the situation ever arise.

It was the second weakness that made the situation not simply life-threatening but a death trap. The Underground had no mechanical means to circulate air, fresh or otherwise. No air-conditioning. No fans. Air moved through the tunnels and the stations as a result of the movement of the trains, forcing dead air up and out at stops and other ventilation points, sucking new air into its wake.

While the cars on the Underground were constructed with fire-resistant and fire-retardant materials, gasoline can ignite dirt. With three trains set ablaze on the three busiest London lines, all within minutes of one another, the tube had come to a violent and convulsive halt. Cars evacuated into tunnels that swiftly filled with roiling clouds of dense black smoke, an orgy of burning plastics that in turn spawned their own toxic gases. While counterterrorist and emergency service personnel responded as best they could, as fast as they could, civilians succumbed to the lethal mixture of poisonous air and their own panic.

King's Cross, which had seen a fatal fire in 1987 that claimed thirty lives, suffered the worst, as dozens of riders were trampled to death in the panicked attempt to flee the station. • An added tragedy came to light in late August, when The Guardian ran an article citing an uncirculated report commissioned by the Home Office through the Security Services at the request of the Government. The report had been undertaken specifically to determine what, if any, exploitable weaknesses existed in the public transport systems in and around London, and it had concluded that the Underground-despite massive counterterrorism measures taken in the past-was still vulnerable to "a coordinated attack directed against those traits unique to the system."