An officer of the Board may enquire into a partnership return if he gives notice of his intention to do so ("notice of enquiry")—
(a) to the partner who made and delivered the return, or his successor,
(b) within the time allowed.
A return which has been the subject of one notice of enquiry may not be the subject of another, except one given in consequence of an amendment (or another amendment) of the return under section 12ABA of this Act or in consequence of the referral of a dispute about the return under section 12ABZB(3) of this Act.
An enquiry extends to anything contained in the return, or required to be contained in the return, including any claim or election included in the return and including anything included in the return by virtue of section 12ABZB(7)(b), subject to the following limitations.
If the notice of enquiry is given as a result of an amendment of the return under section 12ABA of this Act—
(a) at a time when it is no longer possible to give notice of enquiry under subsection (2)(a) or (b) above, ...
(b) after a final closure notice has been issued in relation to an enquiry into the return, or
(c) after a partial closure notice has been issued in such an enquiry in relation to the matters to which the amendment relates or which are affected by the amendment,
the enquiry into the return is limited to matters to which the amendment relates or which are affected by the amendment.
If the notice of enquiry is given as a result of the referral of a dispute under section 12ABZB(3) of this Act—
(a) at a time when it is no longer possible to give notice of enquiry under subsection (2)(a) or (b) above,
(b) after a final closure notice has been issued in relation to an enquiry into the return, or
(c) after a partial closure notice has been issued in such an enquiry in relation to the matters to which the dispute relates or which are affected by it,
the enquiry into the return is limited to the matters to which the dispute relates or which are affected by it.
The giving of notice of enquiry under subsection (1) above at any time shall be deemed to include the giving of notice of enquiry—
(a) under section 9A(1) of this Act to each partner who at that time has made a return under section 8 or 8A of this Act or at any subsequent time makes such a return, or
(b) under paragraph 24 of Schedule 18 to the Finance Act 1998 to each partner who at that time has made a company tax return or at any subsequent time makes such a return.
In this section "the filing date" means the day specified in the notice under section 12AA(2) of this Act or, as the case may be, subsection (3) of that section.