The top rate of 40 per cent will affect 3.25 million people this financial year — up by 56 per cent from barely more than two million when the Conservatives left office in 1997.

Calculations carried out for The Times by the Institute of Fiscal Studies, using recent Revenue & Customs figures, show that if the Chancellor had raised tax allowances to keep pace with rising earnings over his decade at the Treasury, just 220,000 more people would now face higher rate tax compared with 1996-97.

Instead, Mr Brown’s decision to raise tax allowances only in line with inflation, or less in some years, has fuelled an explosion in the number of people hit by 40 per cent tax, allowing him to take at least £3 billion a year in extra revenues.

Among workers now caught by top-rate tax are many university lecturers, and tens of thousands of civil servants and local government officers. Most of them paid the basic rate when the Tories left power.

The ranks of top-rate taxpayers now take in specialist nurses, sisters and modern matrons, police inspectors, hospital doctors with up to five years’ experience, and senior officers in the ambulance and fire services, most of whom would have faced a much lower basic rate tax before 1997.

Since 1996-97, average earnings have climbed by about 54 per cent. But Mr Brown has raised the threshold at which people become liable for higher-rate tax by 31 per cent, according to PricewaterhouseCoopers, the accountants.

In the financial year 2006-07, higher rate tax is pay-able by anyone making more than £38,335. But James Browne, an IFS economist, calculates that top-rate tax would apply only to earnings of £44,175 or more if tax allowan-ces had been raised to keep pace with wages and salaries across the economy.

The same trends mean that an extra 3.5 million people have become liable for income tax at all rates since Labour won office in 1997, based on the Revenue’s own estimates. Even the number of pensioners paying tax has risen by 1.1 million, to nearly 4.4 million since 1997.

The Treasury argues that the rising number of people paying all rates of tax, and higher-rate tax in particular, is a symptom of rising living standards. A Treasury spokesman said: “Successive governments have increased income tax allowances in line with inflation since 1977. Families with children are on average £1,550 a year better off as a result of the tax and benefit measures introduced since 1997.”

However, higher-rate tax hits earners in Britain at a lower level relative to average pay than in many countries. Top-rate tax in Britain kicks in when people make at least 1.3 times average earnings, according to figures from the Organisation for Economic Co-operation and Development. That compares with 1.4 times in Germany, 2.6 times in Spain and 2.7 times in France.

Council Tax bills to rise by 3.5%