About 10 years ago I read this book about small people (they were a different race than humans I think) who are living in a big English or American city. They hide from normal people and live in lost buildings or subway tunnels. I remember that the story was about some problems they had with the police or something.
This is the Borribles – a trilogy of books by Michael de Larrabeti. It features runaway children who become 'Borribles' (match: 'small people') in London ('big English … city') and live in abandoned houses ('lost buildings'). They hide from the police who they call 'Woollies'.
Their rivals are the 'Rumbles' who are a rather obvious parody of the Wombles (down to the names of their leaders).
Marketed as a young adult book, but very dark in its atmosphere and theme.
One of my favourite series and I own a copy on my shelf (not the new covers which look awful and ignore the fact that Borribles wear caps to hide their pointy ears). Would make a great TV/film series.