Ratings agency head to quit

The president of ratings agency Standard & Poor's is stepping down just weeks after the credit rating agency cut the US' top 'AAA' rating and sent global markets into turmoil.

US officials lashed out at S&P after it docked the country's credit rating from 'AAA' to 'AA+' - accusing the agency of committing a trillion-dollar mathematical error and of using a faulty baseline.