8(1)Where—
(a)a case for the opinion of the court is stated under section 56 of the [1970 c. 9.] Taxes Management Act 1970 (as applied by paragraph 1 of Schedule 2 to this Act) in respect of a determination by the Special Commissioners on an appeal under paragraph 5 above ; and
(b)in the proceedings on the case so stated, or in any proceedings arising out of those proceedings, any matter which was determined by the Special Commissioners on that appeal is finally determined otherwise than in accordance with their determination on that appeal,
the following provisions of this paragraph shall apply.
(2)Any expenditure allowable under section 3 or 4 of this Act, which, if the decision of the Board on the claim to which the appeal under paragraph 5 above related had been in accordance with the final determination of that matter, would have been allowed by that decision, or allowed by it as qualifying for supplement under section 2(9)(b)(ii) of this Act, shall be treated for the purposes of this Part of this Act as having been allowed by the Board on the claim to the extent that it has not been previously allowed on the claim, and as having been so allowed to that extent on the date on which the original notice of appeal was given under paragraph 5 above.
(3)There shall be made in any computation made under section 2 of this Act and in any assessment to tax or determination all such adjustments or further adjustments as are necessary in consequence of the final determination.
(4)Any tax which becomes payable in consequence of any adjustment made under sub-paragraph (3) above in an assessment for a chargeable period shall carry interest at the rate of 9 per cent, per annum from four months after the end of that period to the date of payment.
(5)For the purposes of this paragraph a matter shall not be deemed to be finally determined in any such proceedings as are mentioned in sub-paragraph (1)(b) above until a determination thereof made in any such proceedings can no longer be varied or overruled by the order of any court.