Separate return-period assessments under sales tax law cannot be merged into one order; estoppel cannot validate an ultra vires assessment.

A taxing statute that treats each prescribed quarterly return-period as a separate unit of assessment does not permit one consolidated assessment order covering several periods. A notice may refer to multiple defaulted periods, but it cannot confer power to merge distinct assessment periods. Estoppel could not cure the defect, because there is no estoppel against statute and an ultra vires assessment remains a nullity. On limitation, the demand under section 11(2a) was tested by reference to the assessee's accounting year, and the notice was within time; recovery proceedings were not required to conclude within that same period.

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Issues: (i) Whether the assessing authority under the Bengal Finance (Sales Tax) Act, 1941 could make one consolidated assessment order covering several quarterly return-periods. (ii) Whether the plea of estoppel arising from a consolidated return could validate such a consolidated assessment. (iii) Whether the demand in the later matter was barred by limitation under section 11(2a).

Issue (i): Whether the assessing authority under the Bengal Finance (Sales Tax) Act, 1941 could make one consolidated assessment order covering several quarterly return-periods.

Analysis: The Act fastens liability with reference to turnover for the preceding year, but assessment and recovery proceed on the basis of the prescribed return-period. The definitions of "turnover", "year" and "return-period", together with sections 10 and 11 and the rules governing quarterly returns, show that the statutory scheme treats each return-period as a separate unit for assessment. A notice under the assessment rules may refer to several defaulted periods, but that does not authorise a single assessment order combining distinct periods. The quarterly return-period here required separate assessments, and consolidation of those periods in one order was inconsistent with the scheme of the Act.

Conclusion: The consolidated assessment order was ultra vires and invalid.

Issue (ii): Whether the plea of estoppel arising from a consolidated return could validate such a consolidated assessment.

Analysis: The petitioner had initially filed separate quarterly returns and the consolidated return was filed only after the assessing authority issued notice for the four quarters together. In any event, a mistaken or consolidated return cannot confer jurisdiction where the statute does not permit a consolidated assessment. There can be no estoppel against a statute, and an ultra vires act remains a nullity even if parties have acted upon it.

Conclusion: The plea of estoppel failed and could not cure the statutory defect.

Issue (iii): Whether the demand in the later matter was barred by limitation under section 11(2a).

Analysis: The limitation under section 11(2a) had to be computed with reference to the assessee's accounting year, not the calendar year, because the Act defines "year" by reference to the dealer's regular accounts. On that footing, the demand notice was within time. The word "assessment" in this Act does not extend to the entire recovery process, and therefore recovery proceedings were not required to be completed within the same limitation period.

Conclusion: The limitation objection was rejected.

Final Conclusion: The assessment proceedings could not be sustained because the statute required assessment to proceed period by period, and the impugned consolidated assessment and all consequential demand proceedings were set aside.

Ratio Decidendi: Where a taxing statute treats each prescribed return-period as a separate unit of assessment, the assessing authority cannot combine multiple return-periods into one assessment order, and an ultra vires assessment cannot be validated by estoppel.

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