Deregulation of the banks was built on two intellectual pillars. One was that regulation was not necessary because banks would self-regulate in order to protect their reputation. Please stop laughing. The other was that regulation would not work because regulators would always be one step behind the bankers. And unfortunately we cannot laugh this one off. Indeed, the technical problems facing regulation are now compounded by political impediments. Green shoots, lobbying by the banks, and turf wars among the regulators have eroded the momentum for action. So if banks cannot effectively be regulated by the authorities, what can be done?

The Turner review came up with two solutions. One is radically to raise the capital requirements of banks so that shareholders have something to lose if management goes wrong. The other is to change incentive payments for managers so bonuses depend on the past three years of performance. The increase in capital requirements makes sense. But the three-year rule is weak. The inherent problem facing shareholders is that incentive payments cannot go negative. However much damage a manager inflicts, wiping out both shareholders and depositors, the consequences cannot be remotely commensurate. As a result, even bonuses with a three-year lag bias the system towards risk-taking. If you thought big bonuses were history you have missed BAB, the new banking mnemonic: yes, Bonuses Are Back.

So how can we avoid another Northern Rock? While shareholders cannot impose genuine penalties, governments can. Fear of jail would discourage excessive risk. Before bankers huff about blunting incentives, yes, I realise that without carrots, bankers will just sit and gaze at the office ceiling. Bankers, set your minds at rest: the introduction of penalties would permit BABEL: that is, the carrots for genuinely smart behaviour could be Even Larger.

The key problem with using the law against bankers has been the difficulty of getting a conviction: surely, the managers of Northern Rock did not intend to profit at our expense. We do not need to set the burden of proof that high. Intention misses the point. Faced with a corpse and a killer, police do not need to prove ill intent: manslaughter sets the hurdle lower than murder. It is enough to show the killer was irresponsible. That is the standard we need; we need a crime of managing a bank irresponsibly: in other words, bankslaughter.

On Turner's proposal a manager can still benefit from recklessness – as long as the bank does not blow up within three years. After that, if the bank crashes he can be off playing golf. With bankslaughter, when the bank blows up – even if it is a decade later – a criminal investigation traces back to determine whether crucial decisions were reckless. If a reasonable banker faced with the information available at the time would not have taken those risks, the person responsible is dragged off the golf course and jailed.

Once bankslaughter was on the books, bonuses would be less dangerous. Managers would have to weigh the balance between risk and return and take defensible decisions. I doubt hyper-caution would be a problem: the overly cautious would not get bonuses. Surely we can rely on our bankers to exhibit the necessary degree of greed.

Bankslaughter would target the wild fringe rather than the average banker. The wild fringe matters: sometimes it generates a crisis that becomes systemic. We now know that as early as 2004, the Bank of England anticipated that Northern Rock would implode. Its business model was so risky that other banks had not adopted it. But in the short term, reckless behaviour looks smart, and so wiser management teams were coming under pressure to emulate it. By the time of its demise, the Rock was doing a fifth of British mortgages.

By curtailing the wild fringe, bankslaughter would complement Turner's approach, which is to make the average bank behave better. Both are needed. Turner's concern about performance is manifestly necessary. But the crisis has revealed that some banks are more rotten than others. In Britain, the two Scottish banks and Northern Rock were pioneers of imprudence. In Ireland two banks run by an alliance of construction firms and politicians swept the country to ruin. Even if shareholder capital is at risk, some banks are likely to suffer because of poor corporate governance.

Had bankslaughter been on the books, the management of Northern Rock would now perhaps be in the dock. But, vengeful as we feel, the point of criminal sanction would not be to punish reckless behaviour but to discourage it. If this law had existed, would our financial knights have been so errant?