Key Points:

Labour is being warned that its strategy of attacking the wealth of National Party leader John Key is a "dangerous" one and unlikely to win votes from outside its core constituency.

Mr Key amassed a personal fortune working in the investment banking sector where he rose to head global foreign exchange at Merrill Lynch in London.

The exact size of his wealth is unknown and he will not discuss it. A figure of $50 million has been in the public arena but Mr Key will not confirm or deny it. That has not stopped his political rivals trying to draw attention to his money.

Last week Prime Minister Helen Clark made an obvious reference to Mr Key's wallet when she said the problem with clamping down on anonymous donations to political parties was that there needed to be a trade-off in terms of public fund-ing.

"Because the Labour Party isn't led by me with a $50 million bank account," she said.

Housing Minister Chris Carter has also made a point in Parliament that Mr Key's "very large mansion" in Parnell required two sections to be merged so it could be built, with a third house shifted to make way for an all-weather tennis court.

Mr Carter was using the example to try to discredit Mr Key's push for more affordable housing through freeing up the supply of land.

References to Mr Key's wealth have been sporadic and form part of a wider Labour strategy to discredit Mr Key, potentially opening the way for later claims he gives tax cuts to the rich.

Mr Key is unfazed by the attacks and there is some doubt in political circles over what they might achieve for Labour.

Asked what Labour could potentially gain or lose, Auckland University political scientist Raymond Miller said attacks on Mr Key's wealth were dangerous.

"It's always dangerous because he [Mr Key] makes a great deal of having grown up in a working class home, I believe a state house," Dr Miller said.

"Certainly he lived very modestly when he was a child, and uses symbolic gestures to show that he understands what the working poor are going through."

Dr Miller said Mr Key looked very conscious of his wealth to the point that he tried to do something about it by reaching out to others, such as taking McGehan Close girl Aroha Ireland to Waitangi.

While some people might feel resentful toward others who had "made it", Dr Miller said he did not think the attacks would persuade many people who might be "floating voters" to go to Labour.

The attacks could also be blunted by the likelihood that Prime Minister Helen Clark herself is a comfortable millionaire.

The Prime Minister's entry on the pecuniary interests register lists four properties including her home in Auckland, and during her 25 years in Parliament she has put some money into the generous superannuation scheme for MPs.

According to Quotable Value statistics her Auckland home had a rating value of $720,000 in 2005, while Mr Key's was worth $6.8 million.

Asked about the attacks on Mr Key and her own financial situation, Helen Clark said she wouldn't claim poverty, but she wouldn't claim $50 million either.

"My husband and I are people who have had professional jobs and incomes all our working life, and we don't have children," she said. "So obviously we would be described as comfortable."

She added that her and husband Peter Davis were "not known for high living".

Indeed, in a television interview before the 2005 election the prime ministerial microwave was seen to be used to reheat cups of cold tea.

Dr Miller said Helen Clark was known for living extremely frugally and that was perhaps why Labour hoped to get some mileage out of the attacks on Mr Key.

"In Helen Clark's case she just exemplifies what most middle income New Zealand families do in a lifetime, which is to acquire properties."

Mr Key said whatever the extent of the attacks by Labour, they represented the "politics of envy".

He had made no secret of his successful career but neither had he overtly flaunted it, he said.

"Frankly you have to ask the question what these people [Labour] believe in," Mr Key said.

"What we know is they don't like people who are poor that become wealthy, and they don't like people who are wealthy and stay wealthy - so the only conclusion can be that they want people who are wealthy to become poor and people who are poor to stay poor."

PM's assets

Home in Mt Eden, Auckland
Townhouse, Wellington
Apartment, Christchurch
Investment property, Rodney
Annual salary $360,000
Parliamentary superannuation savings (25 years as an MP)