Gaps in the stone bed supporting the track could have weakened it, perhaps fatally. The train wheels may not have been perfectly round, flat spots would repeatedly hammer the rail. Corrosion in the rail might have been missed by routine checks. Or the constant bending of the rails could have caused metal fatigue somewhere on the line. Any one of these could have caused the track to shear.
Some observers say the poor state of track in Britain is directly related to a lack of investment.
As the technical investigation continues the political repercussions are certain to amount.