Reckless City of London bankers will be "punished" and their days of big bonuses are over.

This was the tough message from Gordon Brown yesterday as the Prime Minister went on the offensive over irresponsible behaviour by "fat cats" in the financial markets.

Just 24 hours after unveiling his £500bn gamble to bring stability to the banking system, Mr Brown berated those whose recklessness had contributed to the global economic crisis.

On a trip to a London school as part of his country tour to explain his rescue package to voters, the PM said: "All the hard-working families I meet value hard work, effort and enterprise but we've got to penalise excessive and irresponsible risk taking.

"This is not about rewarding the kind of irresponsibility that's done so much damage in the US."

Earlier, on GMTV, Mr Brown had delivered a similar message, designed to point the finger of blame directly at certain types in the City.

"I am angry at irresponsible behaviour," he said. "Our economy is built around people who work hard, who show effort, who take responsible decisions, and where there is excessive and irresponsible risk taking, that has got to be punished."

Mr Brown said the banks who signed up to the rescue plan would have to accept that there could be no more huge bonuses for top executives.

"The days of big bonuses are over. One of the conditions of us helping the banks is that we will have to reach an agreement about their executive remuneration," he said.

The Prime Minister attacked the way that the operations of some of the banks had left them dangerously exposed following the collapse of the sub-prime mortgage market in the US.

"Most of this has come out of America and then affected the British banking system. The problem is they didn't know what they were buying from America."

Mr Brown's words were in marked contrast to his comments in the Commons just a day earlier when he refused to back a call by Conservative leader David Cameron to curb the pay of bank executives.

However, when the Prime Minister's spokesman was asked what Mr Brown had meant by "punishing" irresponsible behaviour, he replied: "What we want to see is responsible risk taking rewarded and what we don't want is any irresponsible behaviour." When asked again, he gave the same reply.

The spokesman explained how the Financial Services Authority (FSA), the City watchdog, was currently looking at how the pay structures within banks had encouraged irresponsible behaviour and the extent to which new rules could curb such bad practice. However, he added that Chancellor Alistair Darling had made clear that it was not the UK Government's role to run the banks.

Yesterday, the Centre for Economics and Business Research (Cebr) suggested the effects of the global downturn could themselves do much to curb excessive City pay.

It predicted that the total amount of bonus money paid out in London's financial district this year would fall to £3.6bn, down 58% from last year's £8.5bn bonanza. "With shareholders - likely to include the government in some cases - and the FSA breathing down employers' necks, it is unlikely that we will see bonuses paid on the scale of the past four years in the foreseeable future," said Richard Snook, Cebr senior economist.

However, wealthy bankers will not be the only ones who feel the bonus squeeze; the knock-on effect on local businesses, everything from restaurants to car dealerships, will also be negative.

New registrations of Porsches are already down 27% and Aston Martins are down by 25% compared to last year.

"Clearly, bonuses are going to play a much smaller role in the new world," said Mark Pragnell, its managing director.

Last night, Nick Clegg urged the PM to take steps to remove those senior banking executives, who were involved in the excessive risk taking.

In a letter to Mr Brown, the Liberal Democrat leader proposed that board members of banks should be barred from taking bonuses to stop them following distorted short-term business models.

The letter also called for measures on the structure of executive pay to be introduced for all banks, conditions of the bank rescue package to include that banks only repossess family homes as a last resort and banks be banned from withdrawing credit lines from small businesses.

"The government's rescue package must be used as a starting point to reform the way banks operate to ensure this crisis is never repeated," he added.