Thanks for that. Had forgotten about the fine detail.
In my job I'm well aware that discarded cigarettes, matches, etc, are very poor at setting fire to grease and oil. Try it (but don't blame me if it goes wrong). Someone even told me that you can put out a cigarette in a pool of petrol, but I would be too worried about the fumes to try it myself.
Investigated an underframe fire on a train. Noted the area where it started tended to collect leaves, which on their own wouldn't cause a problem as they would burn out very quickly. However the presence of oil / grease in the area give credence to the same fire starting theory. Clearly they wouldn't let us set fire to a train to prove it, and happened so rarely that putting cameras in the location to catch it happening would be pretty pointless too, so at that point it remained a credible theory. Sounds like something similar at King's Cross. Can't really set fire to an underground station as a test, but that fire starting process is too sensible to ignore.