A one-off tax on bankers’ bonuses is expected to form the centrepiece of Alistair Darling’s make-or-break pre-Budget report today.

The Chancellor’s statement will set the scene for the general election campaign, with Mr Darling explaining how the Government plans to slash its record £175bn-a-year borrowing by half by 2014.

A new super-tax of around 50 percent is expected to be levied on City bonuses over £25,000, due to be paid in the coming weeks. Ministers are keen to address public anger over the prevalence of the bonus culture, despite the billions of pounds of public money spent on bailing out troubled institutions.

Ken Clarke, The Shadow Business Secretary, said that plans for a tax on banker bonuses was a distraction from the key issue of how to deal with the deficit.

He said he shared the public anger for bankers, but added of the plans to tax their bonuses: “It’s all tinsel really – because they will pay themselves in other ways.”

“It’s just the sort of stuff that Gordon and Peter have insisted the chancellor, who they didn’t want to be chancellor, put in,” he added.

He said serious spending plans were needed and a strategy to protect quality in key areas.

“You’ve got to do it by getting more for less. You’ve got to stop the process of pouring money over, which Gordon Brown indulged in,” he said.

“A credible path for getting out of deficit and debt in a reasonable time – that’s the key thing.”

Other options open to Mr Darling include raising capital gains tax, inheritance tax or even VAT. With the public finances in such dire straits, he could also freeze income tax thresholds, drawing some 70,000 more workers into the 40% tax band.

Although he will not announce a full spending review today, Mr Darling is likely to give some broad outlines of cuts and efficiency savings planned over the coming years.

He may have to open his speech by upgrading his estimate of the deficit for 2009-10 to £180bn, after official figures showed the Government had already borrowed almost £87bn by October and was on course to overshoot his Budget prediction of a £175bn shortfall.

Harriet Harman said that the City of London has been important to Britain “since the days of Dick Whittington” but after the public finances bailed out banks, there cannot be a return to “business as usual”.

“Since the days of Dick Whittington of the City of London ages ago, our financial services and the City of London has been important”.

She added that “the government have said that when the public finances have stepped in to support the whole finance sector … that we can’t have a situation where it’s back to business as usual.”

Meanwhile, the City continued its efforts to dissuade Mr Darling from introducing the super-tax, with a new report suggesting financial firms paid £61.4bn in taxes in the year to March.

The PricewaterhouseCoopers report, commissioned by the City of London Corporation, revealed financial services firms contributed 12.1% of the Treasury’s total tax take.

Stuart Fraser, policy and resources chairman of the City of London Corporation, said: “There is always a tipping point where changes in the business environment – both in terms of regulation or taxation – begin to affect a country’s competitiveness and damage the ability to attract top talent, which may choose to move to rival financial centres instead.”

This year’s tax take from financial services firms is however £6.4bn below two years earlier, mainly due to lower corporation tax paid on profits.

And the tax take has also been dwarfed by the scale of the public support needed to stave off a financial collapse.

Last week the National Audit Office (NAO) said a mammoth £131bn is expected in total taxpayer outlay on bank bail-outs by the end of this year, including last year’s Northern Rock nationalisation – although the Government should receive £14bn in fees.

The total public sector support – including borrowing guarantees and liquidity support from the Bank of England, as well as savings depositor protection – runs to £850bn, the NAO said.

David Cameron said that he feared the Pre-Budget Report would be a political statement, and called for the government to acknowledge the scale of the deficit.

“This ought to be a day of reckoning but I fear what we will get is a pre-election report rather than a Pre-Budget Report,” he said.

He said the government had been “utterly careless” over the size of the deficit, and called for “a bit of acknowledgement” of its size and the need to tackle it.