Barclays and other banks still fighting Enron-related lawsuits won a significant victory today when America’s highest court ruled that investors could not sue third parties for helping a business to commit fraud.

In a separate case that was widely viewed as a proxy for remaining lawsuits against Enron’s banks, the Supreme Court said a group of investors in Charter Communications could not sue Scientific-Atlanta for allegedly helping the telecoms group inflate its revenues.

Todd Fishman, a partner at Allen & Overy in New York, said the case would deal a significant blow to investors hoping to recover money from other banks.

Barclays, Merrill Lynch and Credit Suisse are among banks that have yet to settle Enron-related litigation.

They are accused of conspiring with Enron to defraud investors in the run up to the energy group’s 2001 collapse.

Several banks accused of the same offence - including JP Morgan and CIBC - have already settled similar cases for billions of dollars.

At the time, US law on whether an investor could sue a third party for helping companies commit fraud was less clear.

Today’s decision - in the case of Stoneridge Investment Partners v Scientific-Atlanta – is the latest in a series of business-friendly Supreme Court rulings that have gradually weakened investors’ power to recover damages for securities frauds.

The Supreme Court ruled in favour of Scientific-Atlanta, the business accused of helping Charter Communications commit fraud by 5 votes to three.

Justice John Paul Stevens, who voted in favour of the investors, said the Supreme Court was engaged in a continuing campaign to undercut investor lawsuits.

J. Edward Ketz, associate professor of accounting at Penn State’s Smeal College of Business, called the ruling "a travesty of justice".

"Investment bankers played a major role in facilitating the fraud at Enron. The court’s decision gives them and other investment bankers a free pass to assist managers in carrying out similar frauds in the future; indeed, in creating new vehicles by which managers can massage the accounting numbers," he said.

Patrick Daniels, a lawyer at Coughlin, Stoia, said the decision marked "a sad day for retirees and pensioners who rely on the integrity of the US markets for their security".

However, Mark Willis, a partner at Cohen Milstein Hausfeld & Toll, a US law firm that represents investors, said: “While this is not the decision we would have hoped for, it is important to remember that cases where a bank or other third-party is accused of helping with a fraud only account for a small proportion of securities lawsuits."

"Investors will still able to claim compensation from companies that engage in fraud," he said.

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