Examination of records. Deficiency assessment. Penalty. Limitation of assessment period.

(b) Except in the case of a wilfully false or fraudulent return with intent to evade the tax, no assessment of additional tax shall be made after the expiration of more than three years from the date of the filing of a return or from the original due date of a return, whichever is later. If no return has been filed as provided under the provisions of this chapter, the commissioner may make such return at any time thereafter, according to the best information obtainable and according to the form prescribed. To the tax imposed upon the basis of such return, there shall be added an amount equal to ten per cent of such tax, or fifty dollars, whichever is greater. The tax shall bear interest at the rate of one per cent per month or fraction thereof from the due date of such tax to the date of payment. No person shall be subject to a penalty under both this subsection and section 12-638c . If, before the expiration of the period prescribed herein for the assessment of an additional tax, a taxpayer has consented in writing that such period may be extended, the amount of such additional tax due may be determined at any time within such extended period. The period so extended may be further extended by subsequent consents in writing before the expiration of the extended period.