(a) has reason to believe that by reason of the omission or failure on the part of the person accountable to submit an account of the estate of the deceased under section 53 or section 56 or to disclose fully and truly all material facts necessary for assessment, any property chargeable to estate duty has escaped assessment by reason of under- valuation of the property included in the account or of omission to include therein any property which ought to have been included or of assessment at too low a rate or otherwise, or

(b) has, in consequence of any information in his possession, reason to believe notiwithstanding that there has not been such omission or failure as is referred to in clause (a) that any property chargeable to estate duty has escaped assessment, whether by reason of under- valuation of the property included in the account or of omission to include therein any property which ought to have been included, or of assessment at too low a rate or otherwise. he may at any time, subject to the provisions of section 73A, require the person accountable to submit an account as required under section 53 and may proceed to assess or re- assess such property as if the provisions of section 58 applied thereto.