Legal disputes exist on whether the coming baby of Duke and Duchess of Cambridge has the right of succession to the British crown.

In 2011, the British parliament amended the Act of Settlement, the ancient law of royal succession, to allow the first baby of Prince William and Princess Kate, male or female, to be third in line to the British throne, following Prince Charles and Prince William.

In the past, if the first baby of the British royal family was a girl, she would not be first in line to the throne. Her younger brothers would be in front of her, according to the Act.

Although that law was changed by the British parliament in October, 2011, more procedures are needed to decide whether the coming royal baby, if it turns out to be a girl, has the right of succession.

According to Professor Robert Hazell, Deirector of Constitution Unit of University College London (UCL), since the British sovereign, that is Queen Elizabeth II, is also the nominal state head of 15 other commonwealth countries including Australia, Canada, New Zealand and Jamaica, etc., the coming royal baby can be a completely legitimate inherit of the crown, only when other 15 member countries make changes to their constitutions too.

British Prime Minister James Cameron has already been negotiating with leaders of commonwealth countries on this issue since two years ago. Yet, the problem still remains unsettled till today.

For Australians, "they don't disagree with the principle of the change. The difficulty is it's an argument between the Australian Federal government and the six Australian states," said Professor Hazell.

"And the Australian states say they still have a direct relationship with the British Crown. And they have the right to change their own laws independently of the federal government in Australia. What they agree to do is a compromise that the six states will formally invite the Australian federal government to change the law and they will recognize that change."

While in Canada, disagreement also exists between the federal government and its French-speaking Quebec.

"Quebec is thought to be very anti-monarchist. It's the French speaking part of Canada with a very strong republican tradition. And so the Canadian federal government is anxious to try to avoid having to consult the provinces. So in Canada, the federal parliament passed very minimalist law, recognizing the change made by the British parliament in Westminster. And that's now the subject to the court challenge in Canada, where a group of people mainly from Quebec have challenged that law, saying it's constitutional."