“(1) Where a person— (a) has accounted to the Commissioners for VAT for a prescribed accounting period (whenever ended), and (b) in doing so, has brought into account as output tax an amount that was not output tax due, the Commissioners shall be liable to credit the person with that amount.… (2) The Commissioners shall only be liable to credit or repay an amount under this section on a claim being made for the purpose. (2A) Where— (a) as a result of a claim under this section by virtue of subsection (1) or (1A) above an amount falls to be credited to a person, and (b) after setting any sums against it under or by virtue of this Act, some or all of that amount remains to his credit, the Commissioners shall be liable to pay (or repay) to him so much of that amount as so remains.… 3 (7) Except as provided by this section, the Commissioners shall not be liable to credit or repay any amount accounted for or paid to them by way of VAT that was not VAT due to them.”