Seeking Space, Well-to-Do Londoners Dig Deep

"Britain is not immune from the housing slump, and London is still reeling from last month's riots. But never mind. In a city that has some of the richest people and most expensive real estate in the world, well-off homeowners who have exhausted the traditional methods of home expansion -- build up, or build out -- are enthusiastically branching out the only other way possible: down."