BAA, the UK airports operator, is the subject of a fascinating rumour doing the rounds in the City that reveals much about the impact of credit derivatives on modern companies and their financing.

The tale goes that the company has asked Standard & Poor’s, the ratings agency, to withdraw its rating for BAA, which was downgraded to junk-status in November last year, specifically to help the company avoid being included in the iTraxx Crossover index when the next series is constituted in March.