Could Andrew Mountbatten-Windsor be removed from the line of succession?

The place of Andrew Mountbatten-Windsor, former prince and brother of the king, in the line of succession to the British throne appears to be under threat in the United Kingdom.

Currently, Mountbatten-Windsor is eighth in line (after the families of princes William and Harry) to the Crowns of the United Kingdom and Australia. This makes it extremely unlikely he would ever become monarch, but his removal is more a symbolic act of repudiation.

Is it possible to remove him? The short answer is yes — but it would most likely be a time-consuming process involving many parliaments passing legislation.

Does the same line of succession apply here?

At the time of Australia's federation in 1901, the British Crown was described as "one and indivisible". Queen Victoria exercised constitutional powers over all her colonies, acting on the advice of British ministers.

That changed after the first world war, due to a series of Imperial Conferences, with the self-governing "dominions" (Australia, Canada, New Zealand, South Africa, the Irish Free State and Newfoundland) having separate Crowns by 1930. This meant the Australian prime minister could advise the monarch about the appointment of the governor-general of Australia and other federal (but not state) Australian matters.

However, the rules of succession to these separate Crowns remained the same. They are a hotchpotch of English laws, including common law rules of inheritance and statutes, such as the Bill of Rights 1689 and the Act of Settlement 1701.

These laws became part of Australian law in the 18th century, but for a long time Australian parliaments had no power to alter them. This changed in 1931 with the enactment of the Statute of Westminster. It gave the dominions power to repeal or alter British laws that applied in their country.

However, recognising this could cause havoc in relation to succession to the Crown, a clause was included in the preamble to the statute, making it a convention that "any alteration in the law touching the Succession to the Throne" shall require the assent of the parliaments of all of the dominions and the United Kingdom. Section 4 of the statute continued the power of the UK parliament to legislate for a dominion, but only if it gave its request and consent.

In 1936, when King Edward VIII abdicated, the UK parliament enacted a statute to alter the rules of succession to the throne, to exclude any children he might have. Australia assented to the British parliament extending its law so it applied to Australia too.

That option is no longer available since the enactment of section 1 of the Australia Act 1986. It says that no act of the UK parliament shall extend as part of the law of the Commonwealth, or a state or territory. Any changes made to the operation of the laws of succession to the Crown of Australia must be made in Australia.

How could Australia change the law of succession?

When the Commonwealth Constitution was enacted, the Crown was still "one and indivisible". This meant no one inserted a section giving the Commonwealth parliament power to make laws about succession to the Crown. However, the framers of the Constitution were clever enough to insert a mechanism to deal with such unanticipated developments.

Section 51(xxxviii) of the Constitution says the Commonwealth parliament may exercise a power, at the request or with the concurrence of all the states directly concerned, which only the UK parliament could have exercised at the time of federation. This means the Commonwealth and state parliaments can cooperate to change the rules of succession to the Crown of Australia.

This issue arose in 2011, when the various realms (being countries that retained Queen Elizabeth II as head of state) agreed to change the rules of succession so that males would no longer be given preference over females, and heirs would no longer be disqualified for marrying a Catholic.

The UK parliament enacted the Succession to the Crown Act 2013 to give legal effect to this change. However, it delayed commencing the act until other realms had enacted their changes too. The British act only made the change with respect to the Crown of the United Kingdom.

Some realms accepted they needed to change the law in relation to their own Crown. Others concluded they didn't need to act, because their Constitution makes their sovereign the same person who is king or queen of the United Kingdom. Legislation was ultimately enacted in Australia, Barbados, Canada, New Zealand, St Kitts and Nevis, and St Vincent and the Grenadines.

In Australia, each state enacted the Succession to the Crown Act 2015. The Australian process took a long time, due to different legislative priorities and sitting periods, and the intervention of state election periods.

Australia was the last to enact its law, after which the alteration in succession was brought into effect simultaneously across all the realms.

How would the process operate today?

If it were proposed to remove Mountbatten-Windsor from the line of succession today, the UK government would probably first seek the agreement of all the realms. While not legally necessary, it is important if a shared monarch is to be retained for all realms to be consulted.

The UK parliament would then prepare its own bill, providing a template for other jurisdictions. This means the changes are uniform across the realms. The bill would probably also specify whether Mountbatten-Windsor's exclusion affects his heirs, princesses Beatrice and Eugenie, and their children. Under the old law, a person who married a Catholic was treated as "dead" for the purposes of succession, so that their exclusion from the succession did not affect the hereditary position of their heirs. The same approach might be taken in relation to the exclusion of Mountbatten-Windsor.

The same parliaments that enacted laws in relation to the last change of succession (apart from Barbados, which is now a republic), would also need to enact an equivalent law, if they wish to maintain symmetry in such rules across the realms. Putting such a bill before a parliament runs the risk that other issues will be raised, opening broader questions concerning the role of the monarchy in different realms.

Could Australia make such a change on its own?

While Australia could unilaterally enact a law to exclude Mountbatten–Windsor from succession to the Crown of Australia, it is unlikely it would do so. There are two reasons for this.

First, it involves a lot of legislative hassle, getting seven parliaments to enact a law that will probably have no substantive effect, given how far Mountbatten-Windsor is down the line of succession.

Second, covering clause 2 of the Commonwealth Constitution says that references to "the Queen" in the Constitution shall "extend to Her Majesty's heirs and successors in the sovereignty of the United Kingdom".

There is considerable disagreement about whether this is just an interpretative provision about updating references, or whether it has a substantive effect.

Keeping Australia's rules of succession in sync with those of the United Kingdom avoids opening that potential Pandora's box.

Anne Twomey is professor emerita in constitutional law, University of Sydney. This piece first appeared on The Conversation.