Standard & Poor's has followed up its announcement, earlier this month, of revisions to its criteria for assessing the ratings of banks' hybrid capital instruments by downgrading a large number of hybrid instruments. Westpac and Macquarie Group have been caught up in the move.Westpac said that S&P's review had led to a one notch downgrade to its tier one hybrid capital instruments. As a result, Westpac hybrid capital instruments issued prior to January 2013 (Basel II instrumens) have dropped from BBB+ to BBB. Westpac hybrid capital instruments issued after January 2013 (Basel III instruments) have dropped from BBB to BBB-.Westpac said its issuer credit rating remains unchanged at AA- and its tier two subordinated debt ratings also remain unchanged.Macquarie said that Macquarie Income Scurities and Macquarie Income Preferred Securities have dropped from BBB- to BB+, and Macquarie Preferred Membership Interests have dropped from BB+ to BB.S&P's new ratings criteria have hit more than 1300 securities around the world.S&P said: "We now deduct an additional notch for Basel III tier one capital instruments for Asia-Pacific banks because we believe that there is greater potential for coupon non-payment on a going concern basis when the regulatory capital conservation buffer under Basel III and other regulatory core equity capital buffers apply."With today's rating actions, we believe our ratings of hybrid capital instruments are better positioned for the potential risk of increased loss absorption, given regulatory and market trends."