Clearstream, the settlement arm of Deutsche Börse and the German exchange group's largest revenue source last year, has become the latest exchange sector business to be hit by the US sub-prime crisis after suffering a sharp downturn in settlement activity last month as share trading slowed.

Clearstream, which is a wholly-owned subsidiary of the German exchange group, suffered a 27% slump in its international business, which fell to 2.33 million transactions last month, and a 20.7% decline in domestic settlement volumes, which dipped to 6.63 million transactions.