Former colleagues of Bill Winters, the London-based head of investment banking at JPMorgan Chase who was ousted last week, today told how he shunned risky and complex investments that crippled the financial markets because they did not make sense.

John Fullerton, a JPMorgan executive, told Bloomberg: “I remember him explaining that they'd looked at these for years and couldn't understand how the economics worked. Despite the tremendous pressure all round them to do it, they didn't do it because the math didn't work.”

JPMorgan got through the financial crisis without suffering a quarterly loss and the investment bank is now having a record year.

Despite the success, Winters, who had been with JPMorgan since 1983, was forced out by chief executive Jamie Dimon last week.

Fullerton said: “Bill's departure is a clear loss and given JPMorgan's scale and complexity it's not a plus for the stability of the financial system.”

Adrian “Buzz” Doherty, another former colleague, said: “He was very often a step ahead of people who had many more years' experience.”