NZ supports changes to royal succession - Key

New Zealand would support moves to change the royal line of succession rules and allow a first-born daughter to become Queen, Prime Minister John Key says.

Under the current law, male heirs accede to the throne before any older sisters.

Britain's Deputy Prime Minister, Nick Clegg, who is responsible for constitutional reform, is looking at ways of changing the rule to grant any future princesses born to the couple the same rights as male heirs.

"Prince William and Catherine Middleton might have a baby daughter for instance as their first child, I think most people in this day and age would think it's worth considering whether we change the rules so that that baby girl then could become the future monarch," Mr Clegg told the BBC.

The British monarch is head of state of 16 commonwealth nations and any change to the line of succession would require legislation in all these countries. Discussions with them have started.

Mr Key will visit England and France on a trip scheduled for April 24 to April 30. He will have a private audience with the Queen and the Prince of Wales, and attend the royal wedding of Prince William and Catherine Middleton at Westminster Abbey.

Mr Key said today he was supportive of the succession changes.

"I don't know whether those changes will happen any time soon and I don't know if she (the Queen) will raise it over lunch," he told Breakfast on TV One.

He expected the conversation was likely to focus on New Zealand as the Queen was "passionately interested" and knowledgeable about the country.

Topics would include the Christchurch earthquakes, and how the families of the 29 men workers killed at the Pike River mine on the West Coast last November were doing.

Republican Movement chairman Lewis Holden said while Britain was looking changing the sexist succession rules other discrimination, such as around religion, would remain.

"The changes will keep the position of New Zealand's head of state in the hands of a British aristocratic family on the other side of the world," Mr Holden said.

"We call on the Prime Minister to include the head of state issue - including the succession law - in the constitutional review. The issue of who New Zealand's head of state is should be decided by New Zealanders at a referendum, not by back-room deals in London."

Green MP Keith Locke promoted a bill to allow the head of state of New Zealand to be elected but it failed at its first reading last year.

He said the succession situation should reignite debate.

"They are in a right royal mess. For example, if Britain reformed its law, but couldn't convince all of the other 16 other nations declaring allegiance to the Crown to do likewise, the consequences could be farcical.

"If Kate had a daughter then a son, we could see daughter reigning as Queen of England at the same time as the son was King of Canada or Jamaica or whatever."

It would be simpler for New Zealand to have its own head of state, he said.