Standard & Poor's has placed the credit rating of National Australia Bank's British subsidiary, Clydesdale Bank, on review. S&P has also downgraded several British banks because of the poor outlook of the UK economy.S&P said it had placed the "BBB+ long-term and A-2 short-term ratings of Clydesdale Bank on CreditWatch with developing implications while it assesses the impact of the negative industry risk trend in the context of Clydesdale's de-risking and restructuring initiatives."In July 2012, S&P revised its outlook on Clydesdale in the long term to positive from stable. At the time, S&P said the bank would have a "lower risk profile than historically" once NAB completed the transfer of £6 billion in problem real-estate loans to the balance sheet of the NAB group. This was completed earlier this year.In December 2011, the ratings agency cut the credit rating of Clydesdale to BBB+, from A+ (a cut of three notches on the S&P scale). S&P also then cut the long-term rating of NAB to AA-, from AA, consistent with the downgrade of all of the major banks in Australia.On this occasion, S&P said the industry risks facing the UK's banks were typically higher than those faced by many comparable banking systems. It also said that the sector's overall risk appetite has been relatively aggressive.S&P also noted that the political, media, investor and consumer scrutiny of the banking system, triggered by the exposure of failings during the global financial crisis, has been more extensive than that affecting many other systems, even as regulatory authorities have led significant system-wide improvements, and the banks themselves have undertaken to make material changes to their business models and to their financial profile.Cameron Clyne, NAB's chief executive, said at NAB's half-year profit briefing last month that "subsidiary regulators are quite keen to retain capital within... [Clydesdale Bank]. So I think the goal for us is not have to put more capital in.""I think, given the economy and the state of where they are [at present], it's going to maybe some time before we can strip out substantial capital… Our goal is to try and minimise having to put fresh capital in, that's a start."