What started as a trading scandal at Carnegie, the 200-year-old Nordic investment bank, has developed into the most serious crisis to afflict Sweden’s centre-right government since it was elected a little over a year ago.

It began when three of the bank’s top proprietary traders – all in their early 30s and brimming with Carnegie’s trademark self-assurance – allegedly tried to boost the value of various derivative instruments in their portfolio by manipulating prices.