[1]During the 1920s, as a result of the growing political and diplomatic independence of the various Dominions of the Empire, the Balfour Declaration of 1926 stated that the United Kingdom and the Dominions were: autonomous Communities within the British Empire, equal in status, in no way subordinate one to another in any aspect of their domestic or external affairs, though united by a common allegiance to the Crown, and freely associated as members of the British Commonwealth of Nations.When Canada subsequently gained full independence following passage of the Statute of Westminster 1931, s. 132 was not amended to reflect its changed status.

[4] In 1935, the Parliament of Canada ratified the conventions, and subsequently passed: This change in position followed the Privy Council's decision in the Aeronautics Reference,[8] which declared: There may also be cases where the Dominion is entitled to speak for the whole, and this not because of any judicial interpretation of ss.

This jurisdiction of the Dominion, the Privy Council held, in the Aeronautics case and in the Radio case is exclusive; and consequently, under the British North America Act, the provinces have no power and never had power to legislate for the purpose of giving effect to an international agreement: that, as a subject of legislation, is excluded from the jurisdiction envisaged by section 92.

[10]In his dissent, Rinfret J (as he then was) argued that the conventions were separate and did not arise as a consequence of the Treaty, the 1925 Reference was binding, and moreover that they were not properly ratified at all, declaring: The treaty-making power is the prerogative of the Crown.

It follows from all that I have said that, in my opinion, the draft conventions upon which is based the legislation now submitted to us have not been properly and competently ratified, that they could not be so ratified without the consent of the legislature in each province, both by force of the British North America Act and upon the proper interpretation of article 405 of the Treaty of Versailles; and that, for that reason, the Acts now submitted are ultra vires of the Parliament of Canada.

[14]The Reference served to promote the concept of dual federalism, where the provinces could act as separate communities within a wider political union.

Thus, Lord Atkin in 1937 famously described the respective powers of Parliament and the provincial legislatures as "watertight compartments"....[18] However, the Judicial Committee recognized that particular matters might have both federal and provincial aspects and overlap....[19] Privy Council jurisprudence also recognized that the Constitution must be viewed as a "living tree capable of growth and expansion within its natural limits"....[20] This metaphor has endured as the preferred approach in constitutional interpretation, ensuring "that Confederation can be adapted to new social realities"....[21] [57] The Supreme Court of Canada, as final arbiter of constitutional disputes since 1949, moved toward a more flexible view of federalism that accommodates overlapping jurisdiction and encourages intergovernmental cooperation—an approach that can be described as the "dominant tide" of modern federalism...[22] The Reference expressly left undecided the question as to the extent of the federal power to negotiate, sign and ratify treaties that deal with areas falling within provincial jurisdiction.

[24] This judgment has generated extensive debate about the complications that were introduced in implementing Canada's subsequent international obligations,[25][26] and it has been condemned for being out of touch with Canadian economic and political realities.

[28] An indication that that may eventually happen came in a comment by Dickson CJ in 1987: The history of Canadian constitutional law has been to allow for a fair amount of interplay and indeed overlap between federal and provincial powers.