Well this is one Brit’s take on it:
"Austin Powers: No, this is me in a nutshell: ‘Help! I’m in a nutshell! How did I get into this bloody great big nutshell? What kind of shell has a nut like this?’ "
One of the Canadian constitutional experts can confirm, but I seem to recall that previous discussions here on the board have stated that countries like Canada and Australia designate as their monarchs, whoever the current valid British monarch is, so as soon as the holder of the British throne changes, it changes automatically in the other countries.
I could be wrong though.
I may be wrong here, but I think that it’s neither that (a) whoever is the British monarch automatically becomes monarch of the Commonwealth realms, nor (b) each country adopts the new British monarch as its own as well, but rather (c) all Commonwealth realms including Britain subscribe to the same line of succession under the Settlement Act as amended. Any changes to it (e.g., the occasionally mooted "Let’s skip Charles and go straight to William) would require the common consent of all Commonwealth realms – or of course their opting out of the shared-monarch arrangement, as was the case with the Netherlands in 1702 and Hannover in 1837, to say nothing of the countries that became Republics.
It’s not inconceivable that the UK could decide to unilaterally replace the Act of Succession and choose some other dynast, or abolish the monarchy, without consulting the rest of the Commonwealth Realms; since each realm has its own constitution, they would in theory be unaffected and the monarchy would continue uninterrupted.
However, this would violate the spirit of the Statute of Westminster, and would generally just be a weird situation all around, especially if they were to choose some other member of the House of Windsor as monarch. It would probably be far more feasible for the other current Commonwealth realms to become republics (as many others, of course, already have – Queen Elizabeth is probably the most frequently deposed monarch in history) than for the UK to do so.
Actually, as far as I can tell, the UK and Canada are probably the countries most tied to the monarchy, the UK due to the Commonwealth Realms as discussed, and Canada because any change to the monarchy would require the consent of all the provincial legislatures.
It would violate the letter of the Statute of Westminster, and so would be void.
Huh. I thought the effect of the SW was to prevent the UK from making any changes in the succession to the throne (and thereby affecting other countries), not making any changes in the identity of its head of state (affecting only itself). Could the UK really not become a republic, then, without the consent of all the other Commonwealth Realms, even if it left their headships of state intact?
But the Statute of Westminster is a UK Act of Parliament, and the UK Parliament could amend it, right?
ETA: the passage in question is in the preamble:
Do provisions of the preamble have the full force of law?
If the SW says that the assent of all the Commonwealth Realms is needed to change the law concerning succession, and since the SW concerns succession, the SW itself can’t be amended without their consent either.
I thought it had become sort of understood that once William gets hitched (presumably settling him down), this will happen with Charles’ consent (and probable relief). That is, I thought it was now an open secret that Charles intended to abdicate to William.
Really? I’ve never heard anyone say that. And it’s my understanding that Edward VIII is looked upon with disdain by the royal family for abdicating his duties.
It sounds more like wishful thinking on the part of those who dislike Charles.
I’ve always understood that the UK parliament, at least, and probably a goodly portion of the Royal Family, considered Edward VIII’s abdication with a bit of relief. Wallis Simpson was bad enough as an American commoner and divorcee, but she and Edward seemed also fairly sympathetic to the Nazis (and fascism in general).
At the time, hewing to his duties would have meant forgoing marriage with Simpson (although not necessarily an affairs) and staying out of politics, which would have rendered his personal feelings towards fascism irrelevant.
Charles may be unpopular generally as a personality, but it seems to me that ducking out of the natural order of succession wouldn’t earn him any praise.
Also I believe I’ve read more than once that Elizabeth blames Edward’s abdication fir her fsther’s relatively early death and dye wouldn’t approve of her own successors choosing that path as opposed to just grinning and bearing the slings and arrows.
Given that by the time his mother gives up the ghost, Charles is likely to be pretty old, were probably looking at a pretty short reign anyway, like George IV or Edward VII. And I have heard that ge has already chosen his Reynaldo name – George VIII, with the queen’s approval
Wow, someone who makes more typoes than me! 
Seriously, a good post, acsenray, with one nitpicky error – Prince Charles’s reputed selected regnal name would be George VII, his grandfather having been George VI.
(thanks. I still am working on my typing on a tiny keyboard skills and constantly amazed at things like regnal being autocorrected to Reynaldo. I’ll Blane that for getting the number wrong too, yeah.)
As far as I can see, the doctrine of parliamentary sovereignty, which (amongst other things) forbids one Parliament from binding a future Parliament, means that Parliament can repeal the Statute just like any other act. In any case, are provisions in the preamble rather than the body of an act justiciable?
Wouldn’t this also require an Act of Abdication to be passed in each of the Commonwealth Realms? Which, in Canada at least, would open up a whole big can of worms as matt_mcl has alluded to. When Edward VIII abdicated, his other Dominions all passed their own Acts (the Irish Free State taking the opportunity to pass other constitutional changes and passing the Act of Abdication a day later than the others). So I guess if they’ve done it before, they can probably do it again.
To get back to one of the questions in the OP, while the UK Parliament has no say in the governments of the other Commonwealth Realms, its ties weren’t fully severed until surprisingly recently in Canada (1982), Australia (1986), and New Zealand (1986). In the first two cases, the balance of powers between the federal government and the states/provinces required the consent of the Westminster to change, and thus when the Realms in question finally settled things, required the acts to be passed in both parliaments to finally remove all ties. New Zealand seems to have only theoretically had any ties to the UK, and was able to finally sever ties without Westminster’s approval.
I don’t believe that the the restriction on amending the Act of Settlement set out in the Preamble to the Statute of Westminster is judicially enforceable against parliament.
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This would be wholly inconsistent with the British constitutional principle of the supremacy of parliament. If parliament wished to limit itself in this way it would need to do so clearly and unambiguously. An aspirational statement in a preamble doesn’t do this.
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The preamble doesn’t say that “any alteration in the law touching the Succession to the Throne or the Royal Style and Titles shall hereafter require the assent” of the Dominions; it says that “it would be in accord with the established constitutional position of all the members of the Commonwealth . . . that” such alterations shall require Dominion consent. But the words to the effect of “and therefore they do henceforth require Dominion consent” are conspicuously lacking.
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Contrast the next paragraph in the preamble, which says that “it is [n.b. not “it would be”] 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 . . . otherwise than at the request and with the consent of that Dominion”. That aspiration is given subatstantive effect by section 4 of the Statute (“No Act of Parliament of the United Kingdom . . . shall extend, or be deemed to extend, to a Dominion as part of the law of that Dominion, unless . . . that Dominion has requested, and consented to, the enactment thereof.”) If the statement in the Preamble were directly effective, s. 4 would be unneccesary.
The statement in the preamble about the succession law amounts to a promise, operating on the political and diplomatic level, rather than an obligation, enforceable through legal mechamism. It means no so much that parliament cannot alter the succession without dominion consent, but that it will not.
Of course, if parliament were to amend the Act of Settlement without the consent of the commonwealth realms, then s. 4 would kick in, and the unamended Act of Settlement would continue to have effect as part of the law of Canada, Australia, etc. If nothing more were done the result would be that, sooner or later, the crown would devolve differently in the UK and the commonwealth realms, leading to different monarchs in different countries.
In certain instances, the Privy Coucil is the final Court of Appeal in some Commonwelth countries
I was talking about constitutional modification. After all, Canada has already consented once to an abdication.
Is that still true? It hasn’t been true in Canada for quite a long time, for example.