Sch 9ZD para 33
(1) This paragraph applies where— (a) a person makes an OSS scheme return or a non-UK return for a tax period (“ the affected tax period ”) relating (wholly or partly) to a UK supply, and (b) after the end of the period during which the person is entitled under Article 61 of the Implementing Regulation to amend their return the amount of the consideration for the UK supply increases or decreases. (2) The person must, in the tax period in which the increase or decrease is accounted for in the person’s business accounts, notify the Commissioners of the adjustment needed to the figures in the OSS scheme return or non-UK return (as the case may be) because of the increase or decrease. (3) Where the change to which a notice under sub-paragraph (2) relates is an increase in the consideration for a supply, the person must pay to the Commissioners the difference between— (a) the amount of VAT that was chargeable on the supply before the increase in consideration, and (b) the amount of VAT that is chargeable in respect of the whole of the increased consideration for the supply. (4) Where the change to which an amendment or notice under sub-paragraph (2) relates is a decrease in the consideration for a supply , the amendment or notice has effect as a claim; and where a claim is made the Commissioners must repay any UK VAT paid by the person that would not have been UK VAT due from the person had the consideration for the supply always been the decreased amount. (5) The Commissioners may by regulations specify— (a) the latest time by which, and the form and manner in which, a claim or other notice under sub-paragraph (2) must be given; (b) the latest time by which, and the form in which, a payment under sub-paragraph (3) must be made .... (6) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (7) In this paragraph “ UK supply ” means a scheme supply that is treated as made in the United Kingdom.