In article , Clive Coleman
writes
Otherwise all those points are set to "needed" (causing them to move
if they're currently wrong). One the train passes over each set they
move back to "free" (unless another route is also holding them)
What's the chances that the points freed at Poters Bar, whist the train
was going over them, allowing the first part of the train in the right
direct and the second part by the point being able to move?

None at all, the points "fell apart" because there were strategic bolts
missing.
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"now, the thing you type on and the window you stare out of are the same thing"