Anyone know if there is a convention/good practice when wiring
lighting circuits for halls/stairs/landings in terms of which circuit
they should be placed on.

Personally, I'd prefer to assign rooms to lighting circuits randomly, rather
than have an upstairs/downstairs split. With careful choice, with one
circuit down, the adjacent room/hallway will have light. Far more people die
from falls than die from electrocution, so it follows that the safety risk
of being left entirely in the dark is considered more important. Labelling
to the effect should be clear at the consumer unit. Besides, you shouldn't
really be working on a non isolated circuit. A popped MCB does not count as
isolation.

Christian.