Alistair Darling will try to force a "permanent culture shift" in the City as he announces a one-off punitive super-tax of more than 50% on the bonuses of tens of thousands of bankers as the centrepiece of the pre-budget report.

The chancellor intends his targeted, one-off levy as a clear message that the City has to "start living in the real world" as the financial sector prepares to lavish hefty payouts on its staff.

The new super-tax rate will be aimed at any bonus above a fixed rate, rather than the basic salary of the employee. It is intended to hit many thousands of bankers, but low-paid staff in bank branches will be exempt.

The tax will be set higher than the 50% income tax rate coming in from April for those earning more than £150,000 a year, sources indicate.

The chancellor has been working on the scheme for several weeks, according to Whitehall sources, who strongly denied reports that Darling had been "bounced" into the plan by Gordon Brown.

Darling, not usually regarded as a populist politician, personally decided weeks ago that plans to control bonuses through schemes proposed by the G20 countries would not be enough after he saw plans by Goldman Sachs to set aside £11.4bn for bonuses.

A senior Treasury figure said: "Salaries have got out of hand. They have been paying themselves like football stars. We have got to get them to think through the consequences of what they are doing. We are imposing 'a reasonable man' test on some of these salaries given the exceptional circumstances we find ourselves."

Darling also feels "it cannot be right to bail out RBS only to see the money pour out at the other end in bonuses".

Treasury officials feel they have devised a watertight way to hit bankers' bonuses without large-scale tax avoidance, following advice from leading City lawyers. It is expected they will tax bonuses as an excess sum paid in a month.

But City accountants said there was a strong likelihood of a legal challenge against a punitive tax aimed at one sector of the workforce. Bill Dodwell, head of taxation at accountants Deloitte said: "We have had calls from bankers asking about what action they might take under the Human Rights Act. There's never been a precedent."

Darling's planned tax raid provoked furious opposition in the City today with the British Bankers' Association claiming such taxes were "populist, political and penal". But the chancellor believes suggestions of a mass exodus of bankers are exaggerated. "We cannot be held to ransom by the banks," one source said.

Darling will make it clear on Wednesday that the super-tax will be levied for a limited period, and Whitehall sources said the government wants a "properly supervised and regulated" City to remain successful. "We don't want to cut the City down to size, the City want some certainty and to know the lie of the land. They will be told that," a Treasury source said.

Ministers believe public anger at bank bonuses is justified given the heavy economic price of the recession, and the fact that some banks have made excess profits from the selling of government bonds designed to reflate the economy.

Darling will reveal on Wednesday that the economy shrank by 4.75% this year, pushing the budget deficit to a record £180bn in the 2009-10 financial year.

Opinion polls have shown that the public strongly opposes the six and seven figure bonuses likely to be paid in the City this year. Government sources said some of those working in the financial sector were "living in a different world". Banks needed "to think long and hard" about what they do.

The levy, the first windfall tax on the banking sector since Margaret Thatcher imposed a one-off levy in 1981, will apply to bankers in both UK and foreign banks operating in the City, as long as the banker pays tax in the UK. Lord Myners, the City minister, recently identified 5,000 financiers earning more than a £1m in the sector, but the chancellor will spread the net wider in Wednesday's announcement.

Some banks have argued they are entitled to pay bonuses by virtue of not receiving any financial support from the government. But Darling will argue that without the government bailout of Royal Bank of Scotland and Lloyds, the entire British banking sector would have been at risk of collapse.

The chancellor will stick to his forecast that output will expand by 1.25% next year and then by 3%-plus in the following years. City analysts are sceptical about the economy's ability to grow rapidly from 2011 onwards but the Treasury will point to the strong growth achieved in the years immediately after the downturns of the early 1980s and early 1990s.

David Cameron, the Conservative leader, is urging quicker action on cutting Britain's record peacetime deficit, but Darling will say the economy remains too fragile to permit the Treasury to start reducing the deficit in 2010.

Darling's announcement on Wednesday will include extra help to tackle youth unemployment but will be broadly neutral in its economic impact. VAT will return to 17.5% at the start of next year following the temporary reduction to 15%. There will be tough restraints on public spending, but no offer of a full spending review. "Frontline services" in schools, hospitals and the science budget will be protected, but not the entire budgets in these departments. The health budget is due to grow by 3.2% in the next year.

Darling claims the uncertainty in the economy would have made a spending review pointless even if there was no election next year. The chancellor will also spell out tax breaks to encourage company electric car fleets from 2012 worth as much as £1,000 to the employee and £600 to the employer. The measure is designed to stoke production of larger electric cars being built by Nissan and Renault.