A war of statistical tables in Parliament left National red-faced after even its own figures showed the gap in earnings between New Zealanders and Australians had increased since it took office in November 2008.

Economic Development Minister Gerry Brownlee had said in Parliament on Tuesday that the gap was less than it was when Labour was in power  but yesterday the statistics proved him wrong no matter how they were presented.

Prime Minister John Key produced a table which he said most accurately compared average earnings because it took into account purchasing power parity.

But his own figures showed the gap had increased by $22 in the two years since National took over in 2008. Instead, he said it showed the gap was less than it was at the "maximum point" of Labour's reign  when the gap peaked at $187.60 in 2005.

But it subsequently shrank to $137.89 by Labour's final year in 2008 and had since increased again to $160.25 under National.

Having already presented a table showing the gap in earnings had increased by about $50 since the end of 2008, Labour's David Parker asked Mr Brownlee what the gap was.

After a lengthy explanation, Mr Brownlee said the gap had moved from $314 to $360 and New Zealand workers were now 1.1 per cent worse off comparatively.

After the tax cuts came through in October, the gap between after-tax earnings would shrink from $238 in 2008 and $247 in March this year to $227, he said.

When in opposition, National had also criticised Labour over the "brain drain" and on that front there has been recent good news for the Government  in the year to June an average of 610 New Zealanders left each week to cross the Tasman long term, well down on the 812 who left each week in the year before.