The push was from the dominions themselves. The acts were essentially passed to eliminate any last vestiges of residual legal authority that Britain might have, either via arcane constitutional or case laws. It needs to be seen as a gradual process, rather than something abrupt or cataclysmic. An evolutionary, rather than revolutionary, action.

All these countries became independent, self-governing countries in their own right (in Canada's case, since the 19th century), but still retain the British monarch as head of state, a largely ceremonial role with a few symbolic and traditional powers.

The 1931 Statute of Westminster declared that all these dominions had legislative independence from Britain, stating by law what de facto existed when they became self-governing. But there were still acts and case laws that could, in theory, mean that Britain could still make laws or pass judgments that might supercede those made in these countries. One example is the possibility that someone could still invoke the right to appeal a judgment of one's domestic supreme court to what was known as the "court of final appeal": the British Privy Council or House of Lords.

Canada began the arduous process of patriating its constitution (aka British North America Act 1867) from Britain with the Canada Act 1982, in which Britain revoked any residual legislative authority in Canada. Canada would now "own" its own constitution and any laws that would stem from it. It also enshrined a Charter of Rights in Canada's constitution.

Australia and New Zealand had their own reasons for seeking similar acts, but the Canada Act and the Charter is often cited as an example, or even a template, for former colonies or existing nations who wish to iron out from their constitutions any legal leftovers of British colonial rule.