A politician who does not twist statistics to suit his or her argument is not by definition a politician.

John Key's big attraction, however, has stemmed from being seen to be not indulging in such behaviour.

But yesterday, the Prime Minister revealed he is is as capable of Machiavellian manipulation of the figures as the rest of the pack.

It could be argued that he had no choice but to defend his Economic Development Minister, Gerry Brownlee. But Key's choice of figures was nothing short of outrageous in being so brazenly selective.

Brownlee got into trouble in Parliament the day before by claiming that the income gap between New Zealand and Australia had narrowed since National came to power in 2008.

Labour MPs did their own calculations. Finding their figures contradicted Brownlee's assertion, they sought to ping him, while leaving the Prime Minister with the dilemma of contradicting a senior Cabinet colleague or backing him even though he was wrong.

Loyalty dictated John Key take the support option. To loud guffaws from the Labour benches, Key told Parliament that he had been advised that the gap between gross average weekly earnings in Australia and New Zealand, adjusted for purchasing power parity, was $160.25. "That is certainly a lot less than it was in 2005, when it was $187.60."

Indeed it is. But National did not win the 2005 election. It was elected in 2008 when - according to Key's own figures - the income gap had narrowed to $138.

Since then, the gap has widened by around $22. Without those figures in front of them and still coming to grips with Key adjusting them for "purchasing power parity", all this seemed to pass Opposition MPs by. So Key did it again.

When Labour leader Phil Goff asked why Key and Brownlee were spreading this "misinformation", the Prime Minister kept spreading and fudging.

"One can use a number of data series, depending on which one someone wants to use."

His one - of course - was the most comparable one.

"I might add that not only is the wage gap smaller now than it was in 2003 but it is smaller than it was in 2004, 2005, 2006 and 2007." But not in 2008 or 2009, Prime Minister.

If Key spread misinformation, Brownlee sowed confusion when his turn came to be quizzed by Labour. He responded with a lengthy answer to show how complicated it all was.

Even so, his analysis showed a fall in the relative position of the New Zealand worker of about 1.1 per cent, compared with an Australian worker.

But when Labour's David Parker asked whether Brownlee was confirming the gap had grown, the minister replied, "That would entirely depend on which series the member wants me to answer from."

By this stage, Labour had wised up to what it described as Key's "massaging" of the figures and asked Brownlee to confirm the rorting.

He responded by accusing Labour of cherry-picking the figures that suited its argument. For one Labour wit, however, it was not a case of Labour cherry-picking. It was more one of National "Gerry-picking".