Royal Bank of Scotland, which is being bailed out with £20bn of taxpayers' money, has signalled it is preparing to pay bonuses to thousands of staff despite government pledges to crack down on City pay.

The bank has set aside £1.79bn to cover "staff costs" - including discretionary bonuses - at its investment banking division for the first six months of the year alone. The same division caused a £5.9bn writedown that wiped out the bank's profits for the same period.

The government had demanded that boardroom directors at RBS should not receive bonuses this year and the chief executive, Sir Fred Goodwin, is walking away without a pay-off. But below boardroom level, RBS and other groups are preparing to pay bonuses to investment bankers who continue to generate profits.

The disclosure drew fierce criticism from Vince Cable, the Liberal Democrat Treasury spokesman.

"The government said they would attach strict conditions on bonuses and it is very clear they are doing nothing of the kind.

"The banks are just making complete monkeys of them."

He suggested the government would not have agreed to bail out any standalone investment bank. RBS and others had become "entangled with casino-style investment banking operations", he said.

Despite the continuing financial turmoil and widespread criticism of the bonus culture in the City, the bank is understood to believe the payments are defensible.

A source said: "I think everybody would expect [that those responsible for writedowns] would not get a bonus. But there are people who still made fairly substantial money in other product areas - you cannot just not pay them bonuses, they will just go elsewhere." Asked about the likely bonus culture after taxpayer-funded bail-out, the source said: "If the government does end up becoming a shareholder, RBS is still a listed entity. It remains the board's responsibility to ensure it is run commercially."

Several US politicians have seized on an investigation by the Guardian last month which showed six Wall Street banks - Goldman Sachs, Citigroup, Morgan Stanley, JP Morgan, Merrill Lynch and Lehman Brothers - had set aside $70bn (£42.5bn) in pay and bonuses for the first nine months of the year.

Five are in line to benefit from a $700bn US taxpayer bail-out. The sixth, Lehman Brothers, has collapsed - though not without securing considerable bonus payouts for staff in the US.

Henry Waxman, chairman of the House oversight committee, wrote to chief executives of America's nine largest banks this week asking them to hand over information about their pay and bonus plans.

In his letter Waxman cites the Guardian report and says: "Some experts have suggested that a significant percentage of [bankers' pay] could come in year-end bonuses and that the size of the bonuses will be significantly enhanced as a result of the infusion of taxpayer funds."

Staff costs at RBS's investment banking division include salaries already paid in the first six months of the year, national insurance and profit-sharing contributions as well as funds earmarked for end-of-year bonuses. The sum set aside is 20% lower than the equivalent figure for the first six months of 2007.

Banking sources privately acknowledge that the sight of these bonus accruals may provoke anger. They concede the industry's pay and bonus regime is under unprecedented strain as it fails to reflect profitability, asset writedowns or share price declines.