Wanganui Mayor Michael Laws has called the Geographic Board "cultural zealots " after its decision to consult the public over what the North and South Islands should formally be called.

The board said today it had discovered a lack of formality in the names for the islands.

"Interestingly, while researching this issue, we noted that `North Island' and `South Island' are actually not official names under our legislation, despite their common long-term usage," chairman Don Grant said.

"We therefore want to formalise alternative Maori names and, at the same time, make the naming of the North and South Islands official."

Alternative naming meant that either the English names (North Island and South Island), or the Maori names (Te Ika a Maui for the North Island and Te Wai Pounamu for the South) could be used individually or together.

This differed from dual naming where both names were used together in official documents, such as maps.

The alternative names would allow the board to recognise the historical and cultural importance of traditional Maori names, while still retaining the long-term and commonly used English names, Dr Grant said.

Mr Laws said the move was part of the board's "ongoing attempt to rename New Zealand" and a pointer to the board's political and cultural bias.

"Where else could you go in the world and the locals have actually two different names for everywhere? These people on the NZ Geographic Board are cultural zealots."

Mr Laws has been a vocal critic of the board's move to add spell Wanganui as Whanganui.

He said the referendum on Wanganui's identity and naming would give the board a clear indication of locals' preference.

"But after today's announcement, you can see their agenda. It is political correctness of the worst kind - unthinking, unfeeling and completely immune from any heritage and history that is not Maori. Their bias is obvious."

Dr Grant said the board would be writing to iwi throughout the country in the coming weeks to seek the known traditional Maori names for both islands.

It expected to be able to publicly consult with all New Zealanders on the names in 2010.