In message . 145,
Tristán White writes

But then I got to thinking even more. Had nothing else to do, forgot to
pick up a paper and had left my book at home. If this "driver" was allowing
himself to fall asleep, in full view of his passengers, between every stop,
what happens in the privacy of the tube-driver's cabin?

If the driver falls asleep (or feints, etc.) the train stops. On
manually driven tube trains the master controller requires constant
downward pressure, otherwise the brakes are applied automatically (the
device is traditionally known as the dead man's handle).
--
Paul Terry