For decades, three large credit rating agencies have together sat in judgment over the financial soundness of governments, multilateral organisations and, crucially, companies that borrow in the international capital markets to fund their activities.

The pronouncements of these high priests of finance, along with a few smaller rivals, affect the cost of funds for issuers of debt, and are often enshrined in the regulations that govern what securities can be bought by insurance companies, pension plans and mutual funds. Ratings can single-handedly create or render obsolete particular kinds of securities. A downgrade can even tip countries towards recession or companies towards bankruptcy.