What exactly is short-selling?

The investment practice of short-selling has been banned in the UK, for 29 specific financial shares, until 16 January 2009.

It has been held partly responsible for undermining confidence in the UK's biggest mortgage lender HBOS.

The decision of the Financial Services Authority (FSA) was an attempt to clamp down on some of the extraordinary recent falls in the value of shares in the banking industry.

The experience of HBOS ended with that bank being taken over by Lloyds TSB, but the FSA and the government are clearly worried there may be more examples to come.

So what is short-selling?

It is a technique that sees investors borrow an asset, such as shares, currencies or oil contracts, from another investor and then sell that asset in the relevant market hoping the price will fall.

The aim is to buy back the asset at a lower price and return it to its owner, pocketing the difference.