LONDON BRIEFING:THEY CAN'T say they haven't been warned. So when Alistair Darling unveils his draconian "super tax" on bank bonuses in the House of Commons this afternoon, the centrepiece of his pre-budget report, will Britain's bankers take it on the chin? Admit they had it coming and perhaps even mutter an apology?, writes FIONA WALSH

Silly question; of course they won’t. Even before the chancellor put the finishing touches to today’s speech, the bankers were bleating about the unfairness of it all, demanding “a level playing field” and, once again, threatening to flee the country.

Some even suggested the new “super tax” would breach their constitutional and human rights. Hmmm. Mostly, though, they were on their phone to their accountants to see how they might find a way around the tax.

Full details of the bonus clampdown will not be known until the chancellor reveals them at lunchtime today but what we do know is that it will be a one-off and will be levied on bankers’ bonuses above a certain level rather than on their salaries. The rate will be 50 per cent-plus.

Bashing the bankers is a crowd pleaser and, as the election draws nearer, an added incentive for Darling and British prime minister Gordon Brown to act.

But the bankers have brought this on themselves: whether it be Fred “the Shred” Goodwin’s obscene £17 million (€18.8 million) a year pension or last week’s threat by the Royal Bank of Scotland board to resign if £1.5 billion in bonus payments were blocked, bankers have utterly failed to grasp the extent of the public anger over their excesses.

As the rest of the nation struggles with the consequences of their reckless lending, and the country’s economy struggles to exit recession, life for many in the City of London has returned to normal. At least 5,000 bankers in Britain will earn more than £1 million this year and the year-end bonuses about to be paid out by the financial sector will run into billions. But those bonuses have been built on the billions of pounds of taxpayers’ money that has been poured into the support of the banks, a figure last week estimated by the independent UK National Audit Office to be £850 billion. The scale of the loss to the taxpayer in shoring up the banks will not be known for years, it warned.

There was a reminder yesterday – if one were needed – of the devastation caused by the uncontrolled behaviour of the banks, as thousands of small shareholders in Northern Rock were told they would not receive a penny in compensation for its nationalisation.

The independent valuer appointed by the UK government has concluded that, even if the bank’s assets had been auctioned two years ago, rather than taken under state control, there would have been nothing left over for investors. Indeed, his calculations suggest that not only would the bank have been unable to repay its £25 billion loan from the Bank of England but there would have been a deficit of £5.7 billion.

Banks such as Barclays and HSBC bent over backwards to avoid taking government bailout funds but all banks have benefited from the unprecedented funds poured into the financial system. And bankers are doing very well from the lucrative business of selling government bonds aimed at rebuilding the economy.

As Darling told a gathering of bankers earlier this week: “There wouldn’t be a bank standing today if taxpayers hadn’t put their hands in their pockets.”

He he urged his audience to rejoin the real world: “You have to pass the next-door neighbour test. You have to be able to look at your next-door neighbour and justify what you are doing.”

In the audience was Richard Gnodde, co-head of Goldman Sachs (which is planning bonuses of more than £11 billion this year) and Bob Diamond, president of Barclays, whose bonus payments have in the past reached the heady levels of £20 million.

Diamond was clearly not swayed by the chancellor’s speech. Yesterday he leapt to the defence of the City’s bonus culture, claiming that a super tax would go against the principles laid out by the G20 and would spark an exodus from London to other major centres with more banker-friendly tax regimes.

The threat of a mass exodus is almost certainly being overplayed by the bankers, particularly as the super tax is a one-off. And despite all the posturing, it is only expected to raise about £1 billion – even less if the inventive accountants have their way.

Fiona Walsh writes for the Guardian newspaper in London