Australia's "big four" banks downgraded as ratings agencies rebuild reputations and brace for Europe fallout

As the Europe's debt crisis deepens, Australia's big four banks have been hit with a ratings downgrade.

The revisions come as ratings agencies tighten up their definition of risk after the collapse of Lehman Brothers more than three years ago.

Here's my analysis form this morning's edition of AM.

While the downgrades had been flagged for more than a year, it's more evidence - if more was needed - that banks are operating in an increasingly risky and uncertain world

The moves comes after this week's decision by Standard & Poor's to cut the ratings of 15 banks in Europe and the United States

For Westpac, the Commonwealth, ANZ and the NAB it's down one notch from AA to AA-minus  - that's the fourth highest rating on the S&P scale.

Even so, the "big four" remain among a handful of highly rated banks in the world and S&P made the point that Australian banks are underpinned by "conservative and comprehensive regulation, and the banking sector's very low risk appetite".