Criminal law under the Constitution Act, 1867

Section 91(27) of the Constitution Act, 1867, also known as the criminal law power, grants the Parliament of Canada the authority to legislate on:

27. The Criminal Law, except the Constitution of Courts of Criminal Jurisdiction, but including the Procedure in Criminal Matters.

Section 91(27) is by and large the broadest of the enumerated powers allocated to the federal government.As noted by Estey J. in Scowby v. Glendinning:

11. ...The terms of s. 91(27) of the Constitution must be read as assigning to Parliament exclusive jurisdiction over criminal law in the widest sense of the term. Provincial legislation which in pith and substance falls inside the perimeter of that term broadly defined is ultra vires. Parliament's legislative jurisdiction properly founded on s. 91(27) may have a destructive force on encroaching legislation from provincial legislatures, but such is the nature of the allocation procedure in ss. 91 and 92 of the Constitution. Here we are not concerned with the result in law of the exercise by Parliament of one of its exclusive heads of jurisdiction. Indeed, the converse is the question: what, if anything, is the result in law of legislation by a province where it may be classified as essentially criminal in nature? Basic principles require the conclusion that such legislation is invalid, regardless of any perceived need for its substantive provisions, and regardless of perceived defects or gaps in the federal legislative plan...

The meaning of the phrase "criminal law" was historically a matter of debate. It was first defined by Lord Haldane of the Judicial Committee of the Privy Council, writing in the opinion for the Board of Commerce case, as that area:

"where the subject matter is one which by its very nature belongs to the domain of criminal jurisprudence".

In Proprietary Articles Trade Association v. Attorney General of Canada, Lord Atkin, writing for the Council, rejected this interpretation:

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