US law firm Milberg Weiss has long been the tough kid on the block. Since the 1970s, it has used class action law suits to win more than $30bn in settlements for wronged shareholders and consumers, dominating the field and earning the bitter enmity of its corporate foes along the way.

But now America's biggest securities law class action firm is about to become America's two biggest class action firms. This month, senior partner Bill Lerach and more than 100 attorneys in the firm's US West Coast offices will form their own separate firm, Lerach Coughlin Stoia & Robbins.