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Prime Minister John Key whole-heartedly promoted New Zealand's historic anti-nuclear credentials in his speech at the weekend to the United Nations.

It is an issue that has not been passionately advocated by a National Party leader since former Prime Minister Jim Bolger's opposition in 1995 to resumed French nuclear testing in the Pacific.

As recently as the 2005 election Labour was campaigning on the ambivalence of National's anti-nuclear policy after promises of changing the law by referendum and then only if it had been an election pledge.

Mr Key neutralised the policy after he took over the leadership from Don Brash and since then there has been no technical difference between Labour and National. But his emphasis since then has been on holding the line on the law that was passed by the fourth Labour Government.

It has never been a signature policy of National's and its supporters still openly debate whether to drop the anti-nuclear law in favour of an anti-nuclear policy, as advocated as recently as Friday in a National Business Review column by commentator Matthew Hooton.

Even when United States President Barack Obama delivered his historic speech in Prague in April proclaiming a new drive to rid the world of nuclear weapons, Mr Key's response was less than enthusiastic. He called it simply "a step in the right direction" and "a positive move".

That changed on Saturday with his strongly anti-nuclear speech reflecting the sentiment of most New Zealanders.

Mr Key has clearly seen new benefits for New Zealand in staying at the frontline of the issue, not just in the international forums where New Zealand diplomats have been highly active, but in the political arena too.

John Key's leadership over the anti-nuclear issue is bound to grate with the Labour Party but with a bipartisan policy they have nothing to gain in commenting on it. That would simply look like sour grapes.

Mr Key can expect more cynicism from the left on his strong advocacy of the need for an agreement on climate change, where no such bipartisanship exists.

Mr Key used his speech to confirm that New Zealand would be seeking a seat on the Security Council in 2015-16. It is up for election in 2014.

Labour will back the bid because former Prime Minister Helen Clark announced it herself in 2007.

Mr Key could have decided that New Zealand had other priorities than chasing a fourth stint on the council - the last being in 1993 - but he may have been advised that campaigning for such a post opens up channels that might otherwise be shut.

And being on the right side of the anti-nuclear issue can do New Zealand's standing and chances no harm.