Hi-tech start-ups — often based around the Old Street roundabout — such as Moshi Monsters, last.fm and Swiftkey have enjoyed huge global success, and Mr Bloomberg said the capital’s emergence as a technology powerhouse was threatening New York’s attempt to take on California’s Silicon Valley. “Our competition is only going to be in other cities that have similar kinds of characteristics. And the city that comes to mind is London,” he said at a seminar at law firm Proskauer’s New York office.