In article , The Revolution Will Not
Be Televised writes
They all had facility for 2 pilots, e.g. extra controls could be
fitted to the Halifax and Lanc if neccessary, but basically they had
ceased to be 2-pilot aircraft by 1943.

I'm not sure if they were intended to be operational with two pilots,
I've only ever seen references to an extra set of controls if required,
presumably mostly for training (although all the sources I have suggest
training was done with only one set of controls). Most sources seem to
suggest movement to/from the nose was awkward enough without extra
controls getting in the way.

Even for daylight ops, I'm not sure if a second pilot would have been
carried, maybe the flight engineers would have received additional
training (as some did unofficially from their pilots). I'm not sure when
autopilots became common equipment (1943 perhaps?), they'd take some of
the workload off the pilot.

--
John