Canada's prime minister is among the Commonwealth leaders being consulted on changing the monarchy's succession rules so that a woman with younger brothers can take the throne.

British Prime Minister David Cameron has sent a letter to his counterparts proposing to change British law so that a male heir no longer takes precedence over a female heir.

Right now, for example, if Prince William and Kate, the Duchess of Cambridge, were to have a daughter, followed by a son, the younger brother would succeed William as king.

Cameron sent the letter to the other Commonwealth leaders last month, according to a report in The Guardian.

In his letter, sent last month, Cameron wrote, "We espouse gender equality in all other aspects of life and it is an anomaly that in the rules relating to the highest public office we continue to enshrine male superiority."

A spokeswoman for Prime Minister Stephen Harper said Canadian officials expect to have a good discussion at the upcoming Commonwealth Summit.

"Canada looks forward to working with Prime Minister Cameron and the other realm countries on this matter," Sara MacIntyre said in a statement.

The Commonwealth Heads of Government Meeting will be Oct. 28-30 in Perth, Australia.

Harper has received the letter, an official confirmed to CBC News.

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Harper had been asked about the issue in April in the lead-up to the royal wedding, and said it was not the time for such a debate.

"The successor to the throne is a man," Harper said. "The next successor to the throne is a man. I don't think Canadians want to open a debate on the monarchy or constitutional matters at this time.

"That's our position, and I just don't see that as a priority for Canadians right now at all."

Not easy to change

Rules specifying who inherits the throne, now based on the 1701 Act of Settlement, are not easy to change — particularly because they involve all 16 Commonwealth countries where Queen Elizabeth is head of state.

Cameron's office said in January that discussions have been taking place among the nations involved, but it could be a lengthy process for any change to be approved.

"Amending the Act of Succession is a complex and difficult matter that requires careful and thoughtful consideration," a Cameron spokesman said on condition of anonymity in line with policy.

If an agreement isn't struck, it could be possible that Commonwealth countries such as Australia or Canada might recognize a different king or queen than in Britain, said legal Prof. Noel Cox of Aberystwyth University in Wales.

"That would be quite difficult," he said. "You're getting into fantasy here."