a child joins a gang only to realise that the leader is quite disturbing

[Jessica]

i only remember fragments of this book. the title was only one or two words, but i still cant remember. what i can recall is that this boy meets another boy with a unique name and learns that he is in a gang. he joins the gang and starts digging around for stuff or something. the gang leader ends up pushes one of the gang members of a ledge just for him to break his legs. the boy finally leaves the group, only for the leader to threaten him about his sister. i may have warped the story a little bit, since i read it about 2 years ago. some things i am sure about though is that they are all children in a gang. im sorry if this makes it hard for you to help.

[Rainbowheart]

What type of gang, like an inner city criminal gang?

How old are the characters, are they preteen children or teenagers?

[Lobstergirl, au gratin]

Where and when is it set?
Cover?
Author's gender?

[Jessica]

I think they called the self a gang but were just a bunch of troublemaking kids. They were all about 11-13

[Rainbowheart]

Do you think the book was set in the UK?