(1)If any person who has paid tax charged under an assessment alleges that the assessment was excessive by reason of some error or mistake in a return, he may by notice in writing at any time not later than six years after the end of the year of assessment (or, if the assessment is to corporation tax, the end of the accounting period) in which the assessment was made, make a claim to the Board for relief.
(2)On receiving the claim the Board shall inquire into the matter and shall, subject to the provisions of this section, give by way of repayment such relief (including, in the case of assessment to income tax at the standard rate, any consequential relief from surtax) in respect of the error or mistake as is reasonable and just:
Provided that no relief shall be given under this section in respect of an error or mistake as to the basis on which the liability of the claimant ought to have been computed where the return was in fact made on the basis or in accordance with the practice generally prevailing at the time when the return was made.
(3)In determining the claim the Board shall have regard to all the relevant circumstances of the case, and in particular shall consider whether the granting of relief would result in the exclusion from charge to tax of any part of the profits of the claimant, and for this purpose the Board may take into consideration the liability of the claimant and assessments made on him in respect of chargeable periods other than that to which the claim relates.
(4)If any appeal is brought from the decision of the Board on the claim the Special Commissioners shall hear and determine the appeal in accordance with the principles to be followed by the Board in determining claims under this section; and neither the appellant nor the Board shall be entitled to require a case to be stated under section 56 of this Act otherwise than on a point of law arising in connection with the computation of profits.
(5)In this section " profits "—
(a)in relation to income tax, means income,
(b)in relation to capital gains tax, means chargeable gains,
(c)in relation to corporation tax, means profits as computed for the purposes of that tax.