“(7) Any dispute between a sewerage undertaker and an owner or occupier of any premises in its area as to- (a) whether the undertaker is under a duty by virtue of subsection(1) above to provide a public sewer to be used for any such drainage of those premises as is mentioned in that subsection: ….. shall be determined by the Environment Agency and may be referred to the Environment Agency for determination by either of the parties to the dispute.”