19(1)If at a time when an enquiry is in progress into a return an officer of Revenue and Customs forms the opinion—U.K.
(a)that an amount stated in the return as the amount of multinational top-up tax payable by a member of the group is insufficient, and
(b)that unless the assessment in the return is immediately amended there is likely to be a loss of tax to the Crown,
the officer may by notice in writing to the filing member amend the assessment to make good the deficiency.
(2)In the case of an enquiry that under paragraph 17(2) is limited to matters arising from an amendment of the return, sub-paragraph (1) applies only so far as the deficiency is attributable to the amendment.
(3)In the case of an enquiry in relation to which one or more partial closure notices have been given, sub-paragraph (1) applies only so far as the deficiency is attributable to matters not addressed by those notices.