This subject seems a bit out of place on a model railway forum, you may get more answers on a froum dedicated to the 12"/1ft .
However there are people who work on the real railway in these forums, they seem to be airing their point of view which may or may not satisfy the laymen as it were.
As previously stated the railway system is very safe, after the failed profit before safety years of railtrack post privatisation. Network rail and the rest of the industy has pushed safety to higher standards. To sugest otherwise is wrong.
Is it going to be perfect? No, no system is planes still crash, trains still crash these are facts. As long as heavy bits of metal are moving at high speed with human interaction, mistakes will be made.
This is the crux of the matter, it will probably come down to human error. Did the p-way keep going to the same place and not finding the fault? Did they raise this to there section manager? Did he raise it to his engineer? Did he raise to to the on track monitoring team? At some point there was a brake down in comunication in to why the defect was consistently being reported and no fault being found. When netrwok rail identify the issue it will be addressed and should not happen again.
Or was the risk not identified in the hardware/ softwhare? was this the human errror?
With regards to the loose or missing pandrol clips, the tracks should be patroled once a week and its probably a known fault and with-in the p way standards, if it is a concern by all means raise it to Network Rail.