Labour's secret internal polling reveals National below 40 percent on 38 percent, similar to the latest Newshub Reid-Research poll which had National on 37.4 percent.

Newshub has been leaked three years of Labour's secret internal polling data, the numbers and trends it uses to make key political decisions, affecting everything from leadership changes to policy choices.

The data was not leaked by the Government. Newshub would not normally run an outside poll, but three years of data like this hasn't been leaked to us before.

It shows Labour's record low of 23 percent in July 2017 with Andrew Little flailing as leader. The party's polling then jumped 14 percent when Jacinda Ardern took over and became Prime Minister.

Fast-forward and Labour overtook National when Simon Bridges became leader in February 2018.

National then plummeted below 40 percent when Ardern had her baby in June 2018, but picked up again. The party then dropped again after Bridges' expenses were leaked to Newshub.

It got worse for National, dropping to 38 percent during the Jami-Lee Ross saga. But it soon experienced a jump as Labour dropped over KiwiBuild fails.

Following the March 15 Christchurch terror attack, Labour reached a record high of 47 percent. Its latest poll has National on 38 percent - below the dreaded 40 percent mark.

When asked if National had ever dropped below 40 percent in internal polling, Bridges told Newshub on Tuesday: "No."

It follows a day of bizarre fever-pitch politics, as the parties piled into attacks ads and personal slanging matches.

The Green Party launched an ugly personal attack ad, casting Bridges as a used car salesman who hates the environment.

Bridges said he found it "funny", but added: "I think [the Greens] are feeling the pressure - we've seen unprecedented attacks this week."

The Greens even enlisted the voice of comedian Tom Sainsbury, famous for mocking Bridges and his accent.

Greens co-leader James Shaw said his intention was never to mock Bridges' accent. He said the party was "just trying to find someone who could accurately depict it".

The Greens' ad was a response to a National Party attack ad. Labour did one too. It was supposed to teach National a lesson, but failed miserably. Even the Green Party base found it disrespectful.

"We were trying to use satire to make a point about National's attack ad - it didn't go well so we pulled the ad," Shaw said.

Greens co-leader Marama Davidson wasn't as fussed, labelling the ad "quite funny".

Deputy Prime Minister and New Zealand First leader Winston Peters called out the Greens over the ad. He said it was "not very kind".

But Peters is no stranger to ridiculing Bridges' accent himself. Earlier this year made fun of Bridges' pronunciation of 'China' as 'Choina'.

He also mocked the National leader in July last year over his pronunciation of 'mining' as 'moining'.

Newshub.