Icap acts as a broker between financial institutions trading interest- rate, credit, equity and foreign-exchange products and has grown from start-up to market leader within 24 years. In that time, its share price is nine times higher and its £2.7bn ($4.09bn) market capitalisation is above that of the London Stock Exchange. But a monthly trading update on Wednesday led to a 4.6% drop by its shares. As a bet on the future health of financial institutions, Icap carries a lot of risk.

Icap performs well in volatile markets. Despite Wednesday's drop, its shares have risen 40% since February, partly due to increased hedging and trading volumes through May's sovereign-debt fears and euro-zone bailout package. But evidence of more-normal market conditions in June and a fall in investors' risk appetite have made investors pause. Group revenue rose 8% in the quarter to the end of June, but this year's pretax profit seems likely to hit the lower end of expectations for £336m to £360m.