The protests and squeals of pain from the global securities industry over talk of changing credit ratings scales for complex debt products have probably turned into slack-jawed silence in the wake of “Corrigan III”.

The strongest motivation for those pushing a new ratings scale for mortgage-backed bonds and similar assets, I believe, is that it would show publicly that regulators had forced investment managers to reassess their mandates and set new rules on exposure to such products, as distinct from other rated debt.