London--In a major blow to the insurance industry's most storied brand, Lloyd's of London's insurance market has been downgraded by Standard & Poor's to a "single A" from a "single A-plus." The company's insurance market was downgraded because of its exposure to the World Trade Center disaster. "Lloyd's will bear substantial claims, albeit significantly reinsured, given its prominence in global aviation, large commercial property and the reinsurance business," said Standard & Poor's in a statement. Lloyd's of London does not operate as an insurance company per se, but rather as a network of affiliates and independent agents. The U.S. accounts for 35% of Lloyd's of London's business and is its largest market. Its U.S. marketing is mostly done person to person, through an elite institutional sales force of both independent agents and agents employed by Lloyd's of London.