In the past 18 months, just about every investment bubble in the world has burst. Property has collapsed, equities have plummeted, commodities have crashed, and even fine art isn't fetching the same fancy prices.

But one bubble refuses to burst: banking bonuses.

Even after receiving billions in government money to rescue the industry, whose bonus culture has been nailed as one of the causes of the crisis of 2008, the bankers have slipped right back into their old ways.

And yet the one lesson we can draw from the last year is that all bubbles burst eventually. The bonus juggernaut is staying afloat on a wave of cheap money and taxpayer support. That will be withdrawn one day, and the fallout will be huge.

The banking industry should have transformed itself while it had the chance. It may well be too late for it to try now.

No one can have failed to notice the way that bankers are starting to make mega-bucks again.

Last week, New York Attorney General Andrew Cuomo said in a report that Citigroup Inc., Merrill Lynch & Co. and seven other big US banks paid $32.6 billion in bonuses in 2008, while receiving $175 billion in taxpayer funds. That was 2008, during the depths of the crisis. With the markets stronger, and confidence returning, payouts this year will be even higher.

Goldman Sachs Group Inc. has already boosted compensation and benefits by 33 percent in the first half of this year, setting aside a record $11.4 billion for such payments.

In the UK, so much evidence is mounting that bonuses are running out of control again that the Financial Services Authority, the country's main regulator, has threatened a clampdown. It has warned that "guaranteed" bonuses may well violate its new code of conduct. Chairman Adair Turner told Parliament recently he was concerned the banks were returning to "business as usual" in the way they paid their staff.

Now we are waiting to see what reaction there is in Germany to legal attempts by former Dresdner Bank staff to force bonuses out of the parent company, Frankfurt-based Commerzbank AG. Some of the claims have been settled out of court, and there can be little doubt the bankers walked away with handsome amounts. German taxpayers won't have any trouble concluding that their money is being used to bail out feckless financiers.

All the earnest talk about reforming the system has amounted to very little. There were some good ideas put forward: paying negative as well as positive bonuses, or spreading payments over several years, for example. Yet right now there is little sign of any of them being implemented.

The closer you look, the more bonuses look like a bubble. The price of bankers has become disconnected from real forces of supply and demand - just as the price of dot-com shares were at the height of that mania, or the price of new houses in the US, Spain or the UK at the peak of the housing boom.

People pay the price because everyone else will, not because they think it is really worth it. They shrug, suspend disbelief and argue that the asset in question is exempt from the usual laws of economics for some complicated reason that they don't really have time to explain. And each time, it's great on the way up and nasty on the way down.