Deloitte on Monday became the first Big Four accounting firm to be fined by the US audit watchdog, accepting a $1m civil penalty for violations of auditing standards.

The fine, related to the firm’s 2003 audit of California-based Ligand Pharmaceuticals, a biotech company, was the result of an investigation by the Public Company Accounting Oversight Board, the regulator set up as part of the Sarbanes-Oxley Act in the wake of the Enron and Worldcom accounting and audit scandals.