(1) For the purposes of this section -
"claimant" means a person who submits a valid claim for a repayment amount;
"repayment amount" means an amount which a person becomes entitled to receive from the Commissioners and which is claimed -
(a) within such period (if any) set down in respect of the provision of excise law under which the claim for repayment is made, where this applies, or
(b) in all other cases, within a period of 4 years from the date of payment of excise duty or of any other act or event giving rise to an entitlement to repayment,
but such amount does not include interest payable under this section.
(2) Where a mistaken assumption in the application of a provision of excise law is made by the Commissioners and as a result a repayment amount is payable to a claimant, interest is, subject to section 960H(4) of the Taxes Consolidation Act 1997, payable by the Commissioners on that amount from -
(a) in the case of an overpaid amount, the date that overpaid amount was recei
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