The move by Standard & Poor's to downgrade $453bn (£240bn) of General Motors and Ford debt to junk status was always going to become an event in the market no matter how well flagged. It is not every day that two of the credit market's biggest borrowers are taken down a notch. The carmakers' debt has been used in so many different structured products that some investors were bound to feel a difference.

Markets have been reeling this week with rumours that some hedge funds were wrong-footed by the development. Some which had apparently been shorting GM shares and buying the bonds, were caught out when the shares rose last week following a tender offer by Kirk Kerkorian, the billionaire, and the bonds fell after the downgrade.