Sheila/Liz, I didn't read the full report, but I DO recall that a discarded cigarette was probably to blame as the source of ignition.
However, I recall that the major cause was the lack of scheduled maintenance, i.e. cleaning.

Below the escalator, and others found on the network, was a massive build up of grease, and other flammable rubbish, paper, etc, that had never been removed.

What they call a "ticking time-bomb".