(a)the [Assessing officer] [ Substituted by Act 49 of 1991, s.99 (w.e.f. 1-10-1991).] has reason to believe that by reason of the omission or failure on the part of the assessee to make a return under section 7 for any assessment year or to disclose fully and truly all material facts necessary for his assessment for any assessment year, chargeable interest for that year has escaped assessment or has been underassessed or has been made the subject of. excessive relief under this Act, or
