There have been more than 50 homicides in London in 2018, with many of the victims young people caught up in gang-related violence, AP reported.
The crime wave has drawn criticism of London's mayor, police tactics and government spending cuts.
Metropolitan Police chief Cressida Dick says violent crime is "a long-term problem which requires concerted long-term effort."
But former chief Ian Blair says budget cuts mean there are fewer officers on the beat. He told the BBC on Saturday that "if you take 20 percent of the Met's money away, something gives and the thing that has given is neighborhood policing."