It will be rather less than 0.1% of the population that are affected.
It doesn't work like that though, does it?
If these flaws hadn't been caught and had led to a fatal accident, it would have directly affected a far, far smaller of the population than that. But it would still have been big news, the government would have made statements etc.
Critics of the IEP (800/801) contracts might like to reflect that this fault is down to Agility/Hitachi to solve at their expense, not that of the TOCs.
They will also not be paid for IEP diagrams that are not delivered because of the fault.
It will be more complicated for the 802 fleets (GWR/HT/TPE), depending on what was in the First Group contract for them, so those TOCs may take a cost hit.
I don't suppose anyone can answer this because if someone actually knows the answer they probably can't say, but it would be interesting to know if Hitachi's liability is limited to the cost of repairs and not getting payment for units that can't run, or if they also have any liability for the consequential costs. (E.g. people not travelling when trains
are back in service because they drove on the way out, or deciding not to use the train in future because they've been given the impression that GWR are happy to strand someone away from home so long as they give them a refund).