KEY POINTS:
It has been a long time between personal tax cuts - actually delivered.
Some have been promised but not delivered and some delayed.
Today's tax cuts will be passed into law under urgency tonight or tomorrow to avoid any suggestion that the promise isn't a solid one.
They will be the first since Bill Birch announced a two-stage cut to the middle tax rate in 1996.
In those days there were three rates. The effective middle tax rate was cut in two stages from 28c to 21c but it took until 1998 to take effect.
The second stage was supposed to take effect in 1997 but the $5 billion spending binge in the National-New Zealand First coalition agreement delayed it a year.
When National left office in 1999 the top rate was 33c.
Labour promised to add a new top rate of personal tax, 39c on income over $60,000, that would affect just 5 per cent of personal taxpayers (the previous top rate was 33c on income over $38,000).
It kept its promise but as wages and salaries have grown, the proportion of personal taxpayers now paying the top 39c rate has grown to 11.9 per cent.
Labour's promise to increase the top rate reversed the trend since the mid-80s and 90s towards lowering rates.
Tax cuts in the 1990s were also delivered through adjustments upwards to the threshold at which the middle rate applied - from $30,875 to $38,000 - meaning more income could be earned before the next, higher rate applied.
In the 2005 election year Budget, Finance Minister Michael Cullen promised tax cuts through threshold changes, adjusted for inflation, that were to have started taking effect last month, but he cancelled them last year. That is why he needs to confirm today's ones in legislation.
Whether it is regarded as high or not, the 39c rate is almost half of what the effective top rate was in the 1950s when it was 60 per cent.
Sir Robert Muldoon dropped the top rate to 50 per cent in 1970 but the third Labour Government in the mid-70s put it back up to 60 per cent where it remained until a major review of tax structures in 1982, called the McCaw review.
According to Paul Goldsmith, who has just finished a book on the history of tax, Sir Robert was so sensitive to the perception that the review was to help the rich that he slapped on a new top rate of 66 per cent.
Mr Goldsmith is a former National candidate who also wrote the "corn-beef" biography of Don Brash.
A major tax review led by Rob McLeod in 2001 says that in the early 80s the tax system was failing.
"It was not raising sufficient revenue to meet the Government's expenditure requirements.
"The system was increasingly seen by the public as unfair and lacking in integrity."
The move from progressive taxation (the higher the income, the higher the rate) towards a more proportional (a flatter tax structure) began with Labour's Finance Minister Sir Roger Douglas - now in the Act Party.
GST was introduced in 1986 and the following year the top rate was lowered to 48 per cent.
The fourth Labour Government was strained to breaking point over Sir Roger's proposal for a flat tax of an amount not specified though it was likely to have been below 20 per cent.
The flat tax was canned by David Lange.
The compromise was to lower the top rate to 33c - which remained in place until the new Labour Government's new rate in 2000.
Mr Goldsmith's book title is taken from a Michael Cullen quote: "We won, you lost, eat that!"
It is from the debate on the repeal of the Employment Contracts Act rather than a taxation debate. But Mr Goldsmith said it was "emblematic" of Labour's bold attitude to raising tax in 2000.
Today's Budget will be a new chapter in Labour's tax story.
