Why have so few bankers gone to jail in the wake of the financial crisis? That is a question many ordinary people have asked in the past few years. More surprisingly, the issue even invaded the Oscar ceremonies last month.

The prize for best documentary was handed to the film Inside Job, which covers the financial meltdown. Accepting his award, the director Charles Ferguson delivered a speech which was almost as memorable as Colin Firth’s (albeit not as funny). “Forgive me, I must start by pointing out that three years after our horrific financial crisis caused by financial fraud, not a single financial executive has gone to jail,” he declared, to scattered applause. “That’s wrong!”

Which raises the question: why? Why are men such as Bernie Madoff now sitting in jails, but all those faceless men and women who conjured up subprime loans or dodgy collateralised debt obligations are not? Is it a plot, worthy of an “inside job”? Or is something else going on?