There is where the problem sits "People can not simply be conjured out of the air."
The railway is a heavily staffed organisation often with many people nearby, but fragmentation stops things happening.
Maybe a service like retained firefighters or RNLI volunteers where a call goes out and people respond if nearby via a managed system. This could included Contractors, NR staff and train operational staff.
Is it?
It might be in certain areas, like the big cities, but I can assure you that once you get out of those urban areas that is certainly NOT the case. I know from my own experience that trying to get NR staff to a fault at Ludlow could easily take over an hour.
And as for a "retained team", you have to be joking!!?? For a start where are you going to find enough volunteers to do this, who is going to train them, and ensure that their training is both current and up-to-date, and if they are contractors, who pays, because they won't do it for nothing.