Don Brash says it's "entirely inappropriate" for the Britsh High Commissioner to have expressed regret over the death of nine Māori who were killed when Captain Cook first arrived in New Zealand.
The British High Commissioner Laura Clarke formally made the statement on behalf of the UK Government on Wednesday.
But Brash says Clarke shouldn't be "interfering in a very intensely political debate within New Zealand".
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The former politician took affront at the number of deaths quoted by Clarke, saying there is no evidence that nine people were killed during the first encounters between Captain Cook's crew and Māori .
"The only written account of what happened when Cook arrived is that recorded by James Cook himself in his diary, and his diary suggests that four, possibly five might have been killed," Brash told Newshub.
"Nine is, in our view, an exaggeration."
Cook arrived in New Zealand on a scientific expedition "without any intention of slaughtering people at all."
"To suggest that he came with evil intent as some of the activists are claiming is clearly nonsense."
With Clarke citing nine deaths, the UK Government was essentially backing the group of "activist groups", Brash said.
"She's giving their view of history a credibility which it frankly does not deserve."
Historian Dame Anne Salmond told NZME that the death toll was not agreed on by historians and that "trying to make this a simple matter is extremely unhelpful".
"The fact of the matter is the accounts themselves are confused about how many people died," she said.
But Brash challenged Dame Anne's claims.
"I think she's got a quite distorted interpretation of New Zealand's history," he told Newshub.
"Her interpretation, for example of the Treaty of Waitangi, is quite inconsistent with the interpretation that most New Zealanders - Maori and non-Māori - have agreed on for a very long time."
The British High Commissioner's public statement wasn't just criticised by Brash. Others said it fell short of a genuine apology.
"When it comes to saying a simple word like 'sorry', just say sorry," said Matthew Tukaki from the Māori Council. "Let's get on with life."
Race Relations Commissioner Meng Foon also expressed disappointment with the UK Government.
"They've been waiting 250 years for a regretful apology," he said. "The Crown should apologise properly, so both parties can move on and build nationhood together."
Regardless of the terminology used, Brash says the whole issue of commemorating Cook's arrival is being politicised.
"It's a new development as activist groups are trying to rewrite our history."