As respects each rating area in which a Gas Board will fall to be treated as occupying, during any rate period, a hereditament of a rateable value calculated in accordance with Part I of this Schedule, it shall be the duty of the Board, before the end of the month of October preceding the beginning of that period, to transmit to the rating authority and to the valuation officer a statement setting out particulars of all the matters estimated, calculated and certified for the purpose of computing the rateable value of that hereditament.