Australian firm Piper Alderman has secured a key court victory in a case brought against ratings agency Standard & Poor's (S&P) and Dutch bank ABN Amro by investors who claimed they were misled about financial products.

An Australian federal court this Monday (5 November) ruled in favour of a group of local councils in New South Wales, which brought claims against S&P, ABN and Local Government Financial Services (LGSF) after losing more than 90% of their investment in S&P-rated products created by ABN.

Federal Court Justice Jayne Jagot said that S&P 'misled' investors when it gave its safest credit rating, AAA, to the risky securities, and ruled that ABN knew the ratings were inaccurate.

The verdict in the case – which was backed by litigation funder IMF Australia – has been seen as significant as the first to hold a ratings agency responsible for investor losses from complex financial products, potentially setting a precedent for similar cases in the future.

Together, S&P, ABN and LGSF are liable to pay a total of A$30m (£20m) to the claimants, including losses plus interest and costs. S&P is planning to appeal the verdict.

Piper Alderman represented 12 of the 13 councils on the case, fielding a team of 17 lawyers led by dispute resolution partner Amanda Banton in Sydney.

Banton said: "This is a major blow to the ratings agencies, which for years have had the benefit of profiting from the assignment of these ratings without ever being accountable to investors for those opinions. This judgment will ultimately have the effect of ensuring ratings agencies are accountable and promoting transparency in the ratings process. No longer will rating agencies be able to hide behind disclaimers to absolve themselves from liability."

Clayton Utz acted for S&P, with a group of lawyers led by litigation partners Dean Jordan and Jonathan Slater. ABN was advised by Allens partners Paul Nicols and Jenny Campbell, while the LGFS was represented by Norton Rose partner Stephen Klotz and senior associate Susanna Taylor.

Clifford Chance also took a role advising S&P on UK aspects of the case – the financial products having been developed and rated in London – but was not involved in the court proceedings.

US firm Cahill Gordon & Reindel assisted S&P with American law, with litigation partner Floyd Abrams overseeing the firm's work.

Click here to view the full court ruling.