The loss of the US government’s top-notch triple-A credit rating, if it ever came to pass, would be a hugely symbolic blow to the status of the world’s economic and political powerhouse.

Yet any debate about the merits of the US government’s credit rating comes against a backdrop where the triple-A stamp of approval has less and less meaning for investors. The credit crisis triggered by the huge growth in risky mortgage lending, which has affected banks and investors around the world, has dispelled the myth that a triple-A credit rating is a guarantee of security.