Discuss the constitutional basis for the principle that criminalisation of conduct is exclusively a legislative function. Illustrate with reference to a recent Supreme Court ruling.

Criminalisation — declaring an act or omission an "offence" and attaching penal consequences — is a sovereign act that the Constitution entrusts only to Parliament and the State Legislatures. The executive may enforce penal law; it can never author it. The Supreme Court's August 2026 ruling on the U.P. Gangsters Act restates this basic.

Constitutional basis

• Legislative competence: Articles 245–246 read with the Seventh Schedule — Concurrent List Entry 1 (criminal law) and Entry 2 (criminal procedure) — vest penal law-making in legislatures alone [1].
• Article 20(1): no conviction except for violation of "a law in force" at the time of the act — the maxim nullum crimen sine lege, nulla poena sine lege. If no statute created the offence, nothing existed to be violated [1].
• Separation of powers / excessive delegation: Rules may settle procedure — forms, officers, timelines — but the essential legislative function of defining what conduct is forbidden cannot be delegated to subordinate legislation.

Illustration: Shiv Pratap Singh alias Chinu v. State of U.P. (2026 INSC 894)

• On 20 August 2026, Justices Pardiwala and Vinod Chandran held the U.P. Gangsters and Anti-Social Activities (Prevention) Act, 1986 to be "still-born": it defines "gang" and "gangster" and prescribes punishment, yet creates no offence [2].
• "Gangster" status rested on executive Rules and police "Gang Charts" — the ipse dixit of the executive — offending Article 20(1) [2].
• Proceedings against two practising advocates, one arising from a Bar Association election dispute, were quashed, showing how a status label ("who a person is") replaced provable conduct ("what a person did") [2].
• Significantly, the Act was not struck down wholly; it simply cannot sustain prosecution — the cure lies with the legislature [2].

The ruling is less a rebuke than a reminder: penal clarity is a constitutional duty, not drafting courtesy. Parliament's own Jan Vishwas Act, 2023, which decriminalised 183 provisions across 42 Central Acts [3] and is being carried forward in 2026 [4], shows the same corrective instinct. States should audit special criminal statutes and write offences precisely within the parent Act — securing both effective policing of organised crime and the rule-of-law guarantee of Article 20(1).