Michael Spencer is fond of boats, planes and automobiles, especially Aston Martins. He also fancies Château Cheval Blanc and horseback riding. The founder and proprietor of Icap, the world's biggest interdealer broker, can afford such indulgences: The London Sunday Times, in its 2004 Rich List published last month, proclaimed the 49-year-old Spencer the richest person in the City, London's financial district, with a fortune estimated at £330 million ($606 million). Spencer's annual take-home pay is nothing to sneer at, either -- £4.93 million in 2003, according to Icap's annual report for the fiscal year ended March 31.

But then, the Icap CEO has been having a rather good run of it lately. In the ferociously competitive interdealer-broker world, where single-digit profit margins tend to be the norm, Icap's are 20 percent. The firm's operating profit in the fiscal year ended March 31 surged 38 percent, to £170 million, on a...