Bankers at Goldman Sachs have been accused of living in a parallel universe after the Wall Street firm announced it had set aside £8bn to pay its staff in 2011 – an average of £238,000 each.

Against a highly charged political backdrop in which the government is pledging to tackle top pay, the potential payments sparked anger among unions and were used as fresh ammunition by campaigners calling for a tax on financial transactions.

A spokesman for the Robin Hood Tax campaign said: "When even in a bad year each Goldman employee pockets an average of $367,000 – nearly 10 times the average UK salary – it is proof that banks live in a parallel universe."

The TUC's general secretary, Brendan Barber, said: "Goldman Sachs are brazenly defying their own sliding profits by dishing out pay and top bonuses worth £240,000 a head. This latest example of excessive rewards for mediocrity should give the government the green light to get tough on top pay.

"Ministers should start by putting workers on remuneration committees and making pay and bonuses exceeding £260,000 liable for corporation tax."

Bankers at Goldman will learn in the coming days about the size of their bonuses, which the firm insisted were lower than last year.

The Goldman payouts come amid fresh speculation about the size of the bonus for Stephen Hester, chief executive of Royal Bank of Scotland. He could be handed £1.5m – a headache for the government because it owes 83% of the shares in the Edinburgh-based bank – but RBS stressed no decisions had been made.

The potential scale of the pay deals was revealed as David Cameron prepared to join the growing debate on moral capitalism with a major speech in which he will argue that the Conservative agenda of markets, transparency and mutuality is well-placed to restore and reform a modern form of popular capitalism.

The speech, which will have echoes of his call for radical capitalism with a conscience at Davos in 2009, is intended to show that his politics and his party's history mean it is better equipped to address capitalism's amorality than socialism. Among Cameron's ideas are ways to support co-operatives. In what is being described as "co-ops in a box", he will set out measures to make it easier legally to create them.

Cameron will say that Conservatives instinctively abhor monopolies and protectionism, and regard transparency as the best antidote to bad company behaviour.

The prime minister is not expected to reveal an array of new policies, but is setting out his views before announcements next Tuesday by the business secretary, Vince Cable, on executive pay and proposals to address City short-termism.

Cable received a boost on Wednesday for his proposal to give shareholders more powers to throw out executive pay deals. City fund manager Fidelity put its weight behind his idea for a binding vote on remuneration reports.

The government's potential intervention comes as the US banks, all big employers in the City, report their results for 2011, when the eurozone crisis dampened activity and hit profits.

Goldman Sachs chief Lloyd Blankfein blamed "global macroeconomic concerns" for a 26% fall in full-year revenues to $28.8bn – down 26% – and a near halving in earnings to $4.4bn.

Goldman used more of its revenue (42%) to pay its 33,000 staff in 2011, even after cutting 7% of the workforce, or 2,400 jobs. The total payout per staff member of $367,000 – a figure that includes salaries, bonuses, equity awards and benefits – was down 15% on the the previous year. The actual amount set side to pay staff was down 21% at $12.2bn.

David Viniar, Goldman's finance director, maintained "discretionary" bonuses were down "considerably more than revenues".

The company recently disclosed more about its pay deals in the UK as a result of rules set out by the Financial Services Authority requiring firms to publish pay for "code staff" – those taking or managing risk. Regulatory filings for Goldman Sachs Group Holdings (UK) show that it had 95 code staff in 2010 who had an average pay deal of $6.2m (£4m) in 2010 – and had a further $595m awarded in a one-off mid-year award of shares in 2010.

In his speech, Cameron will also argue that the triumph of the City under Labour was due to Tony Blair and Gordon Brown's determination to create a form of equality through tax credits funded by the excess profits of the City. He will argue for what he sees as a deeper form of social mobility and fairness created through a better educated and skilled workforce.

A key test for the speech will be whether he repeats his Davos attack on a "winner takes all culture" that ends up with the poorest half of the world's population owning less than 1% of the world's wealth.