"Four global banks are intermediaries in 85 percent of OTC derivatives transactions. The same banks dominate prime brokerage. The same banks own large equity interests in the now demutualised exchanges, clearinghouses and even warehouses of the global markets. Naturally, the same banks dominated underwriting of securitised assets. The implications have scarcely been grasped of what this portends in terms of the information asymmetries and the opportunity to manipulate markets without risk.
Each of these roles gives these few banks a view into the positions of market investors. They know who owns what, using what leverage, under what terms, and trading in which markets. Knowing that, the manipulation of prices to impoverish investors and enrich the ruling banks is child's play with a bit of ill-transparent HFT through proprietary dealing desks and connected hedge funds aligned with the firms.
These banks will protest that there are Chinese walls between their trading desks and the market infrastructure they own. The problem with Chinese walls is that they have chinks in them. (Apologies to PC crowd, but it is an old Wall Street joke I'm quoting.) We have seen from what is now reported about securitisations, that these banks structured products to trade against their clients, often colluding with hedge funds to share the profits. Is it likely that when they balance the public interest in market integrity against next year's bonus they become much more altruistic?
In October 2008 the global financial markets crashed. The story in the media is that it was a panic caused by the insolvency of Lehman Brothers. This is not the truth - or at least not all of it. The crash actually followed a $2 trillion margin call by these four global banks on their prime brokerage clients and OTC counterparties - effectively a 30 per cent increase in required margin. It was the margin call that forced liquidation of global portfolios of all asset classes - and particularly the high quality, most liquid asset classes."
http://londonbanker.blogspot.com/2011/05/concentration-manipulation-and-margin.html