Credit Suisse has become the second bank this month to warn the rally in fixed-income capital markets, which has boosted investment banking earnings in the first quarter, is unsustainable and that investment banks will struggle to deliver double-digit return on equity for the year.

Banks, such as Goldman Sachs and Bank of America Merrill Lynch, have so far this year reaped the rewards of a boom in investment grade debt underwriting and rates trading in the first quarter. But while these strong trends have bolstered earnings, analysts are warning investors against being drawn into a 'false dawn'.