(1) For the purposes of making an assessment under this Act, the [Assessing Officer] may serve on any person who has furnished a return under section 7 or upon whom a notice has been served under sub-section (2) of section 7 (whether a return has been furnished or not) a notice requiring him on a date therein to be specified, to produce or cause to be produced such accounts or documents or evidence as the [Assessing Officer] may require for the purposes of this Act and may, from time to time, serve further notices requiring the production of such further accounts or documents or other evidence as he may require.
(2) The [Assessing Officer], after considering such accounts, documents or evidence, if any, as he has obtained under sub-section (1) and after taking into account any relevant material which he has gathered, shall, by an order in writing assess the chargeable interest and the amount of the interest-tax payable on the basis of such assessment.
[(3) If any person--
(a) fails to make a return as required under sub-section (1) of section 7 and has not made a return or a revised return under sub-section (3) of that section, or
(b) fails to comply with all the terms of notice under sub-section (2) of that section,
the Assessing Officer shall, after taking into account all the relevant material which he has gathered and after giving the assessee an opportunity of being heard, make the assessment of the total chargeable interest to the best of his judgment and determine the sum payable by the assessee on the basis of such assessment:
Provided that such opportunity shall be given by the Assessing Officer by serving a notice calling upon the assessee to show cause, on a date and time to be specified in the notice, why the assessment should not be completed to the best of his judgment:
Provided further that it shall not be necessary to give such opportunity in a case where a notice under sub-section (1) has been issued prior to the making of an assessment under this section.]