18(1)This paragraph applies if a return is amended under paragraph 6 (amendment by purchaser) at a time when an enquiry is in progress into the return.
(2)The amendment does not restrict the scope of the enquiry but may be taken into account (together with any matters arising) in the enquiry.
(3)So far as the amendment affects the amount stated in the self-assessment included in the return as the amount of tax payable, it does not take effect while the enquiry is in progress and—
(a)if the Inland Revenue state in the closure notice that they have taken the amendments into account and that—
(i)the amendment has been taken into account in formulating the amendments contained in the notice, or
(ii)their conclusion is that the amendment is incorrect,
the amendment shall not take effect;
(b)otherwise, the amendment takes effect when the closure notice is issued.
(4)For the purposes of this paragraph the period during which an enquiry is in progress is the whole of the period—
(a)beginning with the day on which notice of enquiry is given, and
(b)ending with the day on which the enquiry is completed.