Insider-trading cases are like London buses: You can wait for ages without seeing any at all. And then a whole bunch will come along at the same time.

Last week, the UK Financial Services Authority was pursuing two high-profile investigations into alleged insider-dealing rings. Earlier this month, prosecutors secured a rare prison sentence against a former stockbroker.

Why now? For years, traders in the financial markets stood more risk of getting struck by lightning on the golf course than they did of being arrested for swapping a few share tips on the same fairways. In reality, the regulators are responding to a public mood that has turned hostile to bankers. And they are covering up their own inadequacies. Show trials are just a distraction from far worse problems elsewhere in the system.

The real wrong-doers in the City of London, as the financial district is known, are surely the politicians and regulators who allowed the country to be virtually bankrupted by an overblown, risk-hungry banking industry. A few brokers and hedge-fund managers getting an inside track on which stocks or bonds might be up or down tomorrow won't make much difference.

The crackdown on insider trading by UK regulators is harsh enough to make everyone in the markets feel nervous. Last week, the financial district was rocked by some dramatic arrests.

In one set of raids, executives of the hedge fund Moore Capital Management LLC as well as Deutsche Bank AG and Exane BNP Paribas were arrested on suspicion of insider trading.

In a separate investigation, as many as 11 people may face charges arising out of a probe that started at the London printers working for UBS AG and JPMorgan Chase & Co.

This month, Christian Littlewood, a former banker at Shore Capital Group plc. and Commerzbank AG's Dresdner Kleinwort, was charged with insider trading along with his wife. A week before that, the agency won an insider-trading case against Malcolm Calvert, a former partner at JPMorgan's Cazenove unit.

The rights and wrongs of each case are judged on their merits. Those accused are, of course, innocent until proven otherwise.

So why is London witnessing this sudden increase in law enforcement for insider traders? For years, insider trading wasn't just a largely victimless crime, as many opponents of the laws have argued. It was also mostly unenforced. Most of us following the City reckoned we had more chance of seeing England lift the soccer World Cup before we saw anyone serve time in prison for illicit financial manipulation.

Of course, there may be some simple reasons. The law is the law, whatever you may think of it, and the regulator's job is to identify anyone who breaks it. If they have finally decided to devote more time and resources to making sure the rules are obeyed, then they are to be commended for that.

And the techniques of surveillance are now a lot more sophisticated. One feature of modern life is that mobile phones and e-mails leave an electronic record of whom we talk to, and when. When tips were swapped in the barbershop, it was very hard to prove who said what to whom. With e-mails and mobile calls, you can prove it precisely. With that kind of evidence, it is easier to build a case that will stand up in court.

But surely, there is something more troubling at work.

After the credit crunch, the public mood turned decisively against the financial markets and the people who work in them. Stocks might have recovered, and the bonuses might be flowing again. That doesn't mean the near-collapse of the banking system has been forgotten.

The regulators may well be getting tougher on financial crime because they sense the public wants to see bankers, brokers and hedge-fund managers sent to prison.

Or perhaps the agency is trying to prove its mettle to the Conservative Party, which plans to abolish the FSA if David Cameron wins power.

In any case, the current witch-hunt is overdone. Making a few pounds by trading a stock ahead of a company announcement is much less damaging than inflating a balance sheet, loading it up with sub-prime debts, and then getting taxpayers to pay billions to the bankers who created the mess.

And who is more guilty of misconduct - a few hedge-fund managers who get ahead of the game, or the regulators who failed to notice that a whole series of financial institutions were built on foundations so flimsy that they collapsed as soon as the market turned down?

Under Josef Stalin, the Soviet Union created show trials to distract the masses from the incompetence of the people in charge of the system.

The insider-trading prosecutions look like they are doing something similar - giving the appearance of a crackdown, while leaving the system intact.

If people are going to be punished for the financial crisis of the last few years - which would be appropriate - then we should focus on the real culprits, not just a few scapegoats.

Matthew Lynn is a Bloomberg News columnist. The opinions expressed are his own.