(a) lay, build, operate or expand any pipeline as a common carrier or contract carrier,

(b) lay, build, operate or expand any city or local natural gas distribution network, without obtaining authorisation under this Act:

(i) laying, building, operating or expanding any pipeline as common carrier or contract carrier; or

(ii) laying, building, operating or expanding any city or local natural gas distribution network, immediately before the appointed day shall be deemed to have such authorisation subject to the provisions of this Chapter, but any change in the purpose or usage shall require separate authorisation granted by the Board.