By Ronald Richenburg
Today, Saturday, 11 December 2021, is an important anniversary that no longer receives the commemoration that it deserves, being the 90th anniversary of the Statute of Westminster 1931.  This was an act of the United Kingdom Parliament in which, most importantly, it was explicitly stated that no future act would extend or be deemed to extend to any of what were then known as the British dominions other than at the request and with the consent of the dominion in question. Most of the limitations on the legislative powers of the dominions themselves were also removed.
It was only by a long and complicated process of evolution that the dominions became fully independent states, and one of the most important landmarks in that process was the passage of the Statute of Westminster. Yet it seems that outside the field of constitutional law the statute is little known today, even in the former dominions where it is of particular importance. On the 75th anniversary of the statute, in 2006, the Canadian newspaper The Globe and Mail published on its opinion pages an article with the title “A statute worth 75 cheers”, stating “It is a national disgrace that . . . [the anniversary] will pass with only perfunctory official notice and nothing in the way of celebration.”  And my New Zealand colleagues tell me that they have no recollection of ever learning about the statute in the New Zealand schools.
One reason for the lack of knowledge of the Statute of Westminster may be that the evolutionary process of which it was part was so complicated. In Canada the main national holiday is Canada Day, 1 July, commemorating the coming into force of the British North America Act 1867,  which created the Canadian confederation as “one Dominion under the name of Canada”. (The act is now known in Canada as the Constitution Act 1867.) But the creation of this new entity (albeit consisting originally of just four provinces) can be seen as a national birthday and is perhaps easier to understand and to remember than the gradual evolution of full national sovereignty with concomitant international recognition.
After 1867 Canada began to assert itself more firmly in international affairs and, most significantly, played a major role in World War I. It was chiefly this that enabled Canada to be a separate signatory to the Treaty of Versailles and to be accepted as a full member of the League of Nations.
A similar process occurred in the other self-governing nations of the British Empire, and the Empire itself was increasingly referred to as the British Commonwealth.  By 1931 the nations seen as essentially self-governing were Canada, Australia, New Zealand, Newfoundland (not yet part of Canada), the Irish Free State (i.e. before becoming the Republic of Ireland), and South Africa. Beginning in 1907 they came to be described as “self-governing dominions” and later simply “dominions”. But the word “dominion” was never defined with any precision, and, as described by Peter Oliver, “Without a more precise definition . . . , politicians could simply point to examples of nations that had acquired the status.” 
After 1907 a number of imperial conferences were held, in which representatives of the United Kingdom and the various dominions came together to discuss matters of mutual concern. At the 1926 Imperial Conference the Proceedings  included reports of different committees, one of which was the Inter-Imperial Relations Committee chaired by the Earl of Balfour (Arthur Balfour). The report of this committee contained what has come to be known as the Balfour Declaration of 1926,  which, in reference to the dominions, stated:
They are 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 allegience to the Crown, and freely associated as members of the British Commonwealth of Nations. 
What is particularly interesting is that the declaration did not create any new status (and the committee had no authority to do so) but, rather, seemed to be describing a state of affairs that already existed. This view is supported by the Statute of Westminster itself, the preamble of which specificlly refers to the declarations and resolutions of the Imperial Conferences of 1926 and 1930 and states that
. . . it is in accord with the established constitutional position that no law hereafter made by the Parliament of the United Kingdom shall extend to any of the said Dominions as part of the law of that Dominion otherwise than at the request and with the consent of that Dominion.
But even if the principles of the Balfour Declaration can be seen as constitutional conventions, they would have been unenforcible in the courts, and the Statute of Westminster goes on to state that
. . . it is necessary for the ratifying, confirming and establishing of certain of the said declarations and resolutions of the said Conferences that a law be made and enacted in due form by authority of the Parliament of the United Kingdom.
In addition to ending the authority of the United Kingdom Parliament to pass legislation extending to the dominions other than at their request and with their consent,  the Statute of Westminster also removed most of the restraints on the legislative authority of the dominions. In particular, the dominion parliaments were freed from the restrictions of the Colonial Laws Validity Act 1865,  thus enabling them to pass legislation that was inconsistent with United Kingdom law, and they were also specifically authorised to legislate with extraterritorial effect.
What is also interesting is that certain provisions of United Kingdom law were specifically excluded from the general provisions of the Statute of Westminster. However, this was due not to any reluctance of the United Kingdom Parliament to relinquish control but, rather, to internal considerations within the dominions themselves. So, for example, the British North America Acts 1867 to 1930, which were the basis of the Canadian constitution, were protected in this way. This was chiefly because of fear in Canada that the powers of the provinces might be eroded if the federal parliament could, in effect, amend the constitution. It was not until 1982 that sufficient agreement on an amending procedure was reached, and accordingly the United Kingdom Parliament passed the Canada Act 1982,  giving Canada all remaining constitutional and legislative powers. Similar considerations existed in relation to Australia, and it was only in 1986 that the United Kingdom relinquished all remaining constitutional and legislative powers. 
A countervailing consideration was that in some dominions there were substantial numbers of people who did not want to weaken links to the United Kingdom. Therefore, in s. 10 of the Statute of Westminster it is specifically stated that the key sections of the Act would not extend to Australia, New Zealand, or Newfoundland until those sections (or any of them) were adopted by the parliament of the particular dominion. This turned out to be of no consequence in Newfoundland as, after a financial crisis in 1934, it relinquished its independent status and became a province of Canada in 1949. Australia adopted the key sections of the Act in 1942 with retroactive effect to 3 September 1939 (the date of British and Australian entry into World War II),  and (as stated above) gained full control over its constitution in 1986. New Zealand adopted the relevant parts of the Act in 1947  and assumed full control over its constitution in 1986. 
The above is a very brief and incomplete summary of a very complicated history. There are different opinions about when the dominions should be considered to have become independent states, and it is difficult to ascribe a precise date, but the enactment of the Statute of Westminster was clearly one of the key events.  So, to the 75 cheers offered by The Globe and Mail in 2006, we can certainly add 15 more today.
 Statute of Westminster 1931, 22 Geo.5, c. 4.
 Globe and Mail, 11 December 2006, https://www.theglobeandmail.com/opinion/a-statute-worth-75-cheers/article1329730/. (Author not given. Unclear whether the article is an editorial or an “op-ed” piece.) (Last accessed 8 December 2021 when freely available, but one week later apparently inaccessible without a password.)
 British North America Act 1867, 30 & 31 Vict., c. 3.
 For a discussion of the increasing use of the name “Commonwealth”, see H. Duncan Hall, “The genesis of the Balfour Declaration of 1926”, Journal of Commonwealth and Comparative Politics (1962), Vol. 1, no. 3, pp. 169-193.
 Peter C. Oliver, “Dominion status: history, framework and context”, International Journal of Constitutional Law (2019), Vol. 17, no. 4, pp. 1173-1191. See in particular p. 1175.
 Imperial Conference 1926, Summary of Proceedings, Cmd. 2768. HMSO, 1926.
 This should not be confused with the Balfour Declaration of 1917, which stated the British government’s commitment to support the creation of a Jewish homeland in Palestine.
 Imperial Conference 1926, p. 14.
 Many books on constitutional law, in discussing parliamentary sovereignty (or supremacy) have suggested that this provision is contrary to the doctrine that no parliament can bind its successor, but most of them also state that such a consideration would arise solely in theory and not in practical reality.
 Colonial Laws Validity Act 1865, 28 & 29 Vict., c. 63.
 Canada Act 1982, 1982 c. 11. The relevant part of the act is known in Canada as the Constitution Act 1982 but is still cited with reference to the U.K. act.
 Australia Act 1986, 1986 c. 2. A corresponding (and nearly identical) act, also called the Australia Act 1986 was passed by the Australian Parliament (Act no. 142 of 1985) and took effect on the same day as its U.K. counterpart.
 Statute of Westminster Adoption Act 1942, Act no. 56 of 1942 [Australia].
 Statute of Westminster Adoption Act 1947, Public Act no. 38 of 1947 [New Zealand].
 Constitution Act 1986, Public Act no. 114 of 1986 [New Zealand]. (U.K. legislation was not required for this act to be passed.)
 For a discussion of the time frame in which the dominions attained statehood, see William C. Gilmore, “The acquisition of dominion statehood reconsidered”, Virginia Journal of International Law (1982), Vol. 22, no. 3, pp. 481-517.