Mandatory statutory assessment requirements prevail over conflicting rules, and prior acquiescence does not cure an illegal reassessment basis.

A statutory assessment made contrary to a mandatory provision could not be validated by conformity with a conflicting rule, because the Act prevailed over the rule and the required assessment basis remained binding. An unchallenged original assessment did not cure that illegality or bar reassessment, as the same statutory requirement applied to reassessment proceedings and there can be no estoppel against statute. Prior acquiescence therefore did not legalise a defective assessment, and reassessment could proceed on the statutory footing.

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Issues: (i) Whether a dealer could elect assessment-year basis under Rule 39 where Section 18(4) required assessment on the previous-year basis. (ii) Whether an original assessment made without challenge barred a later reassessment on the ground of illegality in the original assessment.

Issue (i): Whether a dealer could elect assessment-year basis under Rule 39 where Section 18(4) required assessment on the previous-year basis.

Analysis: The governing statutory scheme required assessment in the manner prescribed by the Act, and a return or assessment made under Rule 39 could not override the mandatory requirement of Section 18(4). The first question had already been concluded by prior authority, and the assessment made in contravention of Section 18(4) remained invalid even if it conformed to Rule 39.

Conclusion: The answer was in the negative and against the assessee on the legal proposition, though the practical result on this issue supported the assessee's challenge to the assessment method.

Issue (ii): Whether an original assessment made without challenge barred a later reassessment on the ground of illegality in the original assessment.

Analysis: The unchallenged original assessment did not legalise the defect or confer authority on the department to perpetuate the illegality in reassessment proceedings. Section 18(4) applied to reassessment under Section 21 as well, no separate reassessment procedure was prescribed, and there could be no estoppel against statute. The validity of the original assessment was not required to be finally determined for deciding the reassessment dispute.

Conclusion: The reassessment was not barred by the prior acceptance of the original assessment, and the challenge failed on this issue.

Final Conclusion: The appeal was unsuccessful, and the reassessment proceedings were sustained.

Ratio Decidendi: A statutory assessment or reassessment made in violation of a mandatory provision cannot be validated by prior acquiescence, and there can be no estoppel against the operation of the statute.

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