Complex sentence: Districts exist in English Shire counties, which have a two-tier structure of local government, in which local government functions are divided between county councils and district councils, to the level where they can be practiced most efficiently.
Split into simpler sentences: Districts exist in English Shire counties, which have a two-tier structure of local government. In this system, local government functions are divided between county councils and district councils, to the level where they can be practiced most efficiently.