Where works of improvement have been executed in any slum area or in relation to any building or buildings in a slum area, in pursuance of the provisions of sections 5, 5C and 6, any expenses incurred by the Competent Authority or, as the case may be, any local authority, in connection with the maintenance of such works or the enjoyment of amenities and conveniences rendered possible by such works, shall be recoverable from the occupiers of the area or of buildings concerned as service charges; and if the amount due is not paid within the time specified, it shall be recoverable from the occupier concerned as arrears of land revenue.]