Nearly four hundred thousand more taxpayers have joined the two highest tax brackets since Labour came to power, figures from the Inland Revenue Department show.

The number of taxpayers paying the top rate of tax - 39 cents in the dollar on incomes over $60 000 - has nearly doubled in the eight years the rate has been in effect.

The number of taxpayers in the top bracket has increased from 193 620 in March 2001 to 384 720 in March 2007, an increase of 98.6%.

The amount of tax paid by this group has also increased from $5.8 billion to $11.3 billion over the same period, while inflation has increased by 16.2% and average hourly earnings have increased by 25% (Reserve Bank data)

When the top tax bracket was introduced in 2000, the Labour/Alliance government claimed that only 5% of taxpayers would pay the highest rate.

That figure was 11.7% for the March 2007 year, an increase of 83%.

The Treasury forecasts an even higher figure of 14% for the March 2008 year in the Tax Ready Reckoner on its website. The IRD says that this is an estimate and "comes from Household Survey data (HES), not tax administrative data."

In the other tax brackets movement is also evident. In the $38 001 to $60 000 bracket there were 399 190 taxpayers the year ended March 2001 The IRD reports that in the year to March 2007 there are now 596 180, an increase of 49.3%.

The tax this group paid increased from $4.14 billion to $6.3 billion, a 52% increase over the six years

In the most highly populated bracket, $9501 to $38 000 the number of taxpayers fell by less than one per cent over the 2001 to 2007 period, and in the under $9500 bracket the number of taxpayers fell by nearly 14% to 677 410.

Note: the IRD Data includes all people with a wage or salary income including welfare beneficiaries, children and some people with nil incomes, but excludes people with only investment income where the correct amount of tax was deducted at source.