Every weekday Valdemar Ventura, a gentle man with impeccable manners, leaves his small flat in south London and, until July, made his way to Downing Street and the Cabinet Office, where his duties included cleaning the floors, lavatories and office of the deputy prime minister,Nick Clegg. "A good man," Ventura says. "He always said, 'Hello, good morning'." Acknowledgment matters to a workforce often rendered largely invisible.