S&P warns UK over high debt levelBy Chris Giles and Dave Shellock in LondonPublished: May 21 2009 10:10 | Last updated: May 22 2009 00:52Britain on Thursday became the first big economy to be warned in the financial crisis that it might lose its top-notch credit rating, in a move that raised fears of possible downgrades for other large industrialised nations.Standard and Poor’s lowered its medium-term outlook on the triple A rating for the UK’s debt to “negative” from “stable” for the first time since the credit ratings agency started analy...