This is the latest in ACM's series of reports on the succession.
To access these, click on this icon, "The Succession" on the right hand column of the front page.
The British Prime Minister, David Cameron, has written to the leaders of the other Commonwealth Realms about allowing first-born daughters and heirs who are or who marry Catholics to inherit the throne.
According to Australian Associated Press, the issue has taken on fresh urgency since the marriage of Prince William, the second in line to the throne, to the former Kate Middleton in May. Should their first child be female, she would rank behind any subsequently born male child.
The report says that changes to the law will now be discussed at the Commonwealth Heads of Government Meeting in Perth, Western Australia, from 28 to 30 October, 2011.
Any changes require the agreement of all 16 Commonwealth Realms – the United Kingdom, Canada, Australia, New Zealand, Jamaica, Antigua and Barbuda, the Bahamas, Barbados, Grenada, Belize, St Christopher and Nevis, St Lucia, the Solomon Islands, Tuvalu, St Vincent and the Grenadines and Papua New Guinea.
"Notwithstanding republican reliance on the old succession rules to argue for change to some politicians' republic, no Australian republican Prime Minister has ever bothered to exercise his prerogative to initiate negotiations on changing the law," says ACM Convenor Professor David Flint.
"When the law is changed, which is likely, Australian and other republicans will have one less argument for their politicians' republic."
The first Head of the Commonwealth was King George VI, who was succeeded by Queen Elizabeth II. The office is personal to Queen Elizabeth II and while there is no formal agreement as to whether the office will pass to her heir, Professor Flint says " It is inconceivable that this will not occur."
Under the common law of each of the Realms – an dnot just the law of the UK – succession to the throne is determined by preferring the oldest male of the same rank, or what lawyers call male primogeniture.
In addition, the succession is governed by the Act of Union of 1800 restating the provisions of the Act of Settlement, 1701 and the Bill of Rights, 1689.
Following the reign of King William III and Queen Mary II, the succession is restricted to legitimate descendants of Sophie, Electress of Hanover and disbar those who are Roman Catholics or who have married Roman Catholics.
" These rules seem curious and discriminatory to us, but you have to see them in the context of the time. They were principally to ensure the succession did not go back to the former King, James II or his direct descendants," said Professor Flint.
"James was seen to be under the influence of the enemy, King Louis XIV of France. Indeed he had attempted to introduce an absolute monarchy along French lines into England, and this was unacceptable to the Parliament or the nation.
" According the Bill of Rights spells out the terms of the emerging constitutional monarchy. "
…The Queen's nihil obstat…
A step in the direction of abolishing male primogeniture has been made in the recent Sovereign Grants Act, 2011 under which the first-born child, whether male or female of Prince William and his wife Catherine will inherit the Duchy of Cornwall.
The income of the Duchy maintains the mainly charitable activities of the Prince of Wales.
"I have written to the heads of state, the prime ministers of the other realms concerned. We will be having a meeting about this at the Commonwealth heads of government conference," Mr Cameron said.“It isn't an easy issue to sort – for many of them there may be issues and worries about starting a parliamentary or other legal process.
"But I'm very clear it's an issue that we ought to get sorted and I'd be delighted to play a part in doing that."
Labour MP Keith Vaz urged the prime minister to act quickly, saying: "Does he not agree that it's better that we resolve this matter before rather than after any future royal children are born?"
A government spokesman repeated the warning that it was a "complex and difficult issue – it needs careful thought and consideration".
The Queen has indicated that she has no objection (nihil obstat) to the changes proposed. A spokesman for Buckingham Palace said: "This is a matter for government, in consultation with Commonwealth.”