Profiting from fear
Alistair Darling has just signalled on the Today Programme that he is profoundly uncomfortable with the widespread practice of profiting from the woes of companies perceived as vulnerable through short-selling their shares.
This is highly relevant right now, in that shares in HBOS - our largest mortgage lender - fell by more than 30% at one stage yesterday, which would have been unthinkable a few months ago. And they've fallen again this morning.
If you are running a huge deposit-taker like HBOS you can't dismiss that kind of share-price fall as just one of those things, a stock-market phenomenon that'll pass.
There's always a risk of contagion from equity markets to credit markets.
Or to put it another way, the HBOS chief exec would be anxious (to put it mildly) that those who fund his bank - who lend to it - would get the heeby-jeebies from what he would see as an over-reaction on the stock market to the demise of Lehman.
If you have your savings with HBOS, if you're a money manager that has lent HBOS many tens of millions of pounds, it's hard to shrug off what looks like investors screaming that there's a fire at HBOS.
Those investors may be hysterical, alarmist and misguided. But how can HBOS's creditors be absolutely sure of that?
And if these creditors decided not to hang around to find out, and simply withdrew their credit from HBOS, well that could turn stock-market rumour and speculation into a reality - as no bank can survive as and when it loses the confidence of its creditors.
Which is why the Chancellor was unambiguous this morning that something should be done about speculative short selling, or the practice by hedge funds and others of selling shares that they don't own (shares they've borrowed) with a view to buying them back at a lower price and pocketing the difference.
However he neatly passed the buck to the regulator, the Financial Services Authority, saying that it was looking at how and whether to restrict short-selling in these febrile conditions.
And it won't be easy for the FSA to sort this.
First, short-selling (as I've said many times) is not evil, in and of itself. In fact, short-sellers perform a public service when they take a risk to puncture the over-valuation of assets, as they routinely do.
Second, in global markets it's hard for any single national regulator to take a stand against a practice like short-selling, when investors can simply move their activities offshore.
But it would probably be foolish for the authorities to plead impotence - because the consequence might be a much bigger mess for them to clean up, as and when the short-sellers spark a fully fledged banking crisis.