(1) Section 668 of the Principal Act is amended -

(a) in subsection (3) -

(i) in paragraph (a), by substituting "paragraph (b) and subsection (3A)" for "paragraph (b)" and by substituting "the 4 immediately succeeding accounting periods" for "the 2 immediately succeeding accounting periods", and

(ii) in paragraph (b), by substituting "Notwithstanding paragraph (a) but subject to subsection (3A)" for "Notwithstanding paragraph (a)" and by substituting "the 3 immediately succeeding accounting periods" for "the immediately succeeding accounting period",

(b) by inserting the following after subsection (3):

"(3A) Where a trade of farming is permanently discontinued, tax shall be charged under Case IV of Schedule D for the chargeable period in which such discontinuation takes place in respect of the amount of the excess which would, but for such discontinuance, be treated by virtue of subsection (3) as arising in an accounting period or accounting periods ending after such discontinuance.",

(c) by substituting the following for subsection (4):