The chief executive of ClearBridge Advisors, the underperforming US equity manager that Legg Mason acquired from Citigroup at the end of 2005, is to depart at the end of March, two months after Legg Mason's founder and chief executive stepped down.

Brian Posner has decided to step down as chief executive and co-chief investment officer "to pursue entrepreneurial activities in financial services", Legg Mason said in a statement.