An officer of the Board may enquire into a return under section 8 or 8A of this Act if he gives notice of his intention to do so ("notice of enquiry")—
The time allowed is—
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 9ZA of this Act.
An enquiry extends to—
but this is subject to the following limitation.
If the notice of enquiry is given as a result of an amendment of the return under section 9ZA of this Act—
the enquiry into the return is limited to matters to which the amendment relates or which are affected by the amendment.
In this section "the filing date" means, in relation to a return, the last day for delivering it in accordance with section 8 or 8A.