What is the former name of the rail service to which the Northern City Line belongs?
Northern City Line:  It is part of the Great Northern Route services and operates as the south-eastern branch of the East Coast Main Line (ECML). Great Northern Route: The Great Northern Route (formerly known as Great Northern Electrics) is the name given to suburban rail services run on the southern end of Britain's East Coast Main Line and its associated branches.
Great Northern Electrics