It was a debacle. The large ratings agencies – Moody’s, Fitch and Standard & Poor’s – completely misjudged the creditworthiness of subprime mortgages and bonds backed by them. But while there is an urgent need for change, intrusive regulation would utterly fail to prevent similar problems in future, while imposing considerable costs.

Some have gone as far as blaming the subprime mortgage crash on the ratings agencies because, in retrospect, their judgments were wrong. But a lot of other intelligent people were wrong as well. A separate issue is the report by the Financial Times last week that a computer bug resulted in Moody’s awarding incorrect triple A ratings to billions of dollars-worth of one type of complex debt product. That is something that Moody’s must resolve but it is not the primary basis for wider debate about credit ratings.