In message , Boltar
writes

Also don't forget theres there question of money. Not only the extra
cost of powering the trains in the night but staff wages. I don't
suspect theres a hope in hell of getting *any* LU staff to work night
shifts (who don't have to already past about 1am) without a payrise
never mind the drivers.
I don't know about now, but 30 years ago in my time on Northern and
Central lines, we did work nights. The last and first trains were
operated by the same crews and in winter were sometimes called on to run
snow clearing trains on outside sections.
--
Clive