The funds, through the Managed Funds Association, said the scale of the problem was so great that it could undermine bank rescue plans as tens of billions of dollars would be kept out of the market. It was also likely to lead to the failure of some fund managers, said Richard Baker, chief executive of the MFA.
The warnings come as hedge funds have been quietly shifting billions of dollars of assets out of London to the US, claiming that the US legal system provides greater protection.
Mr Baker, a former congressman, said that by damaging confidence in prime brokers after the fall of Lehman, delays in returning assets were prompting hedge funds to hold more cash and to move assets out of London.