So far as the activities of any wholly-owned subsidiary of Associated British Ports consist of the carrying on of any such undertaking as is mentioned in the definition of " statutory undertakers" in section 290(1) of the [1971 c. 78.] Town and Country Planning Act 1971 or section 275(1) of the [1972 c. 52.] Town and Country Planning (Scotland) Act 1972, that subsidiary shall be deemed for the purposes of any enactment relating to statutory undertakers or statutory undertakings to be such an undertaker carrying on such an undertaking.