Hot on the heels of the Libor scandal and money-laundering at HSBC and Standard Chartered Bank comes the allegation that Barclays Bank attempted to manipulate the US energy markets to make profits. Of course, Barclays has no direct interest in buying or selling oil, gas or electricity. Its aim is to make profits by betting on the price changes, a process that often drives up the price of the underlying commodity and forces ordinary people to pay sky-high prices.

This speculative activity is facilitated by complex financial instruments known as derivatives, described by investment guru Warren Buffett as "financial weapons of mass destruction". Behind the technical jargon lies a giant gambling machine, which bets on anything that can be priced. The hard cash needed to settle the outcome of the bets is always highly uncertain until the contracts mature, which could be 10 to 15 years in the future. And, like other bets, derivatives don't always pay off – as the cases of Nick Leeson at Barings and more recently Jérôme Kerviel at Société Générale exemplify.

The UK government claims that speculation will be curbed by a separation of investment banking from the retail side. This, it is claimed, will protect savers and taxpayers from the toxic effects of risky positions adopted by bankers. This policy will not work. Even after separation, investment banks will continue to use funds from retail banks, pension funds and insurance companies for their speculative activities. The speculators will continue to shelter behind limited liability and dump losses on to innocent bystanders. Unless the benefit of limited liability is removed from investment banks, their losses and reckless risks will inevitably be transferred to other sectors. The separation between retail and speculative operations needs to be accompanied by unlimited liability for investment banking, ensuring that those who take excessive risks are 100% liable for their mistakes.

Derivatives are central to the current economic crisis. In 2008, Lehman Brothers collapsed with 1.2 million derivatives contracts, which had a face value of nearly $39 trillion, though the economic exposure was considerably less. For nearly six years before its demise, almost all of the pre-tax profits at Bear Stearns came from speculative activities. It could not continue to pick winners indefinitely, and collapsed in 2008. It had shareholder funds of $11.8bn, debts of $384bn and a derivatives portfolio with a face value of $13.4 trillion. The derivatives gambles also brought down American International Group (AIG) – the world's largest insurer – and Washington Mutual. Then in October 2011, MF Global, a US brokerage firm that specialised in delivering trading and hedging solutions, filed for bankruptcy. It had nearly 3 million derivatives contracts with a notional value of more than $100bn.

Despite these high-profile casualties, risk-hungry investment bankers remain undeterred. The face value of the global derivatives trade is about $1,200 trillion (£749 trillion). With a global GDP of $65-70 trillion, the world economy is not in a position to absorb even 0.1% ($1.2 trillion) of losses.

The UK's GDP is about £1.5 trillion. Just three UK banks – Barclays, HSBC and Royal Bank of Scotland (RBS) – alone have a derivatives portfolio, with a face value totalling nearly £100 trillion. Barclays leads the way with £43 trillion. It has recently reported a third-quarter loss of £47 million, but its balance sheet points to a more serious position. Barclays' last full-year accounts show assets of £1.56 trillion and capital of only £65bn, meaning that its gross leverage is nearly 24 times its capital base. A decline of just 4% in asset values would wipe out its entire capital. Barclays' balance sheet shows gross exposure to derivatives of £539bn, though the bank could argue that this is offset by hedges of £528bn, leaving a net exposure of £11bn. The difficulty is that the hedges, as Lehman Brothers, Bear Stearns and Northern Rock have learnt, do not necessarily work in the desired way and always depend on the position of the counter parties in a highly unpredictable environment.

Merely separating retail and investment banking will neither choke off nor contain the effects of toxic gambles, because speculative activities will affect other sectors of the economy. For any possibility of containing the crisis, speculative banking needs to have unlimited liability. Thus, if the bets go bad, bankers will personally need to bear the negative consequences. One of the tasks of the banking regulator should be to ensure that the size of the bets bears a reasonable relationship to the assets of the gamblers, so that cavalier bankers are not able to gamble more than they can lose. No retail bank, pension fund, insurance company or pension fund should be able to provide money to any investment bank without specific approval from its stakeholders.

The above reforms will help to reduce speculative activity and quarantine the negative effects of reckless gambling. They will also remind neoliberals that the freedom to speculate needs to be accompanied by responsibilities.