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Commenting on a Herald-Digipoll result this morning which showed support for National rising five points to 50.8 per cent, Mr Cunliffe said Prime Minister John Key and his party were benefiting from being in power for some time and "a temporary upswing in the economy as a result of high dairy prices and an quake insurance payments".
In the poll, National showed no sign of being affected by allegations of a conflict of interest that engulfed high flying minister Judith Collins which gained momentum during the polling period.
However, Mr Cunliffe said he expected that would "filter through" and affect National over time.
"And as it's part of a broader narrative about National and crony capitalism I think National will corrode because New Zealanders do not like the idea that Government ministers are using their position to enrich themselves, their party and their family."
Mr Cunliffe said the poll, which had Labour slipping below the 30 per cent mark, showed "we've got more work to do".
Referring to questions around his use of a trust to receive donations to support his leadership campaign last year, Mr Cunliffe said: "We expected to take a hit, we did and now we're moving on".
"It reflects a particular point in time that's already behind us. We're in a new phase now announcing new policy around our economic direction with an important speech on forestry tomorrow and I think you'll seen in more detail where we're headed."
Mr Cunliffe also expressed some doubt over the accuracy of the poll.
"Our internal polls show us unmoved in the mid- 30s."
Meanwhile, Ms Collins faced further questions about the Oravida affair this morning, particularly around the October dinner in Beijing which she, along with her senior advisor Margaret Malcolm, "close friends" Stone Shi and Julia Xu from dairy and seafood export company Oravida, and a senior Chinese border control official attended.
She said she did not know who paid for the meal.
"I've already said I didn't pay for it. Margaret Malcolm didn't pay for it the taxpayer didn't. I don't know who did and I haven't asked."
Asked whether the fact that it appeared either Oravida or the Chinese official paid for dinner added to perceptions of a conflict of interest, Ms Collins, said: "actually it doesn't", before walking away from reporters.
The fact Ms Collins walked away from questions about the dinner was "not a good look at all", Mr Cunliffe said.
"She should come clean. Who paid for the dinner? Who was the Chinese official? Why did the ambassador not attend? Those are what New Zealanders want to know... they want to know how deep the conflict of interest goes.
"This is a minister who is on the run. Ministers who are on the run can't stay running forever and there's much more to come out on the Collins story. Labour is aware of other matters which will be brought to the public attention in due course."
- By Adam Bennett of the New Zealand Herald