Income escaping assessment. (1) If (a) the Income tax Officer has reason to believe that by reason of the omission or failure on the part of an assessee to make a return of his income under section 22 for any year or to disclose fully and truly all material facts necessary for his assessment for that year, income, profits or gain chargeable to income tax have escaped assessment for that year, or have been 246 under assessed, or assessed at too low a rate, or have been made the subject of excessive relief under the Act, or excessive loss or depreciation allowance has been computed, or (b) notwithstanding that there has been no omission or failure as mentioned in clause (a) on the part of the assessee, the Income tax Officer has in consequence of information in his possession reason to believe that income, profits or gains chargeable to income tax have escaped assessment for any year, or have been under assessed, or assessed at too low a rate or have been made the subject of excessive relief under this Act, or that excessive loss or depreciation allowance has been computed.