Transparency is supposed to be good for the world of finance. Perhaps some of the subprime crisis might have been averted if banks had been more transparent in their off-balance sheet financing. One of the world's most notable warriors against corruption is called Transparency International .

So it is perhaps a surprise to discover that share markets might be more liquid, dealing costs lower and trading more efficient and fairer if there was less transparency when trades were made, not more. At least, that is what supporters of "broker anonymity" say.