There are more than 250 gangs in London and according to the Metropolitan Police, which could be responsible for one in seven of all crimes in the capital.
In the Today programme's Andrew Hosken's first report on South London gangs, he analyses the different gangs in Brixton and the conflicts between them.
Karl Lokko, a former Brixton gang member, told Andrew Hosken that gang members are not "conditioned by life to kill each other".
"It's abnormal", he explains. "They've been fed that lie
that it's kill or be killed."