Institutions that benchmark their entire equity portfolios against big stock indices are riding for a fall, according to Peter Webb, chief executive of Unicorn Asset Management. "There is something wrong when investors take weightings in stocks on the grounds of size alone," he said.

Webb is not alone in thinking this way. For years, active managers have been aggrieved about being forced to have low weightings in small-cap stocks, as a result of being slaves to the index.