All the lights are on in the tower, after a certain time of night there would be compulsory black out during the second world war.
Private Atkins hasn't been educated very well in what information he's allowed to give. He gives his name, rank and branch, refusing to give anything else. Military protocol states you are required to give name, rank and service number (religion can also be given).
It's shown to be raining at the start, yet the soldier's tunic is dry. He'd be soaking wet.