Jeremy Corbyn and Sadiq Khan have each hosted meetings on violent crime amid concerns over the number of killings in London so far this year.
During a gathering in Parliament, Labour leader Corbyn spoke to police officers and experts including John Carnochan from Glasgow's Violence Reduction Unit, which has been praised for the way it deals with the problem.
Meanwhile, London mayor Khan hosted Amber Rudd, the home secretary, and Metropolitan Police Commissioner Cressida Dick at City Hall, where delegates held a minute's silence in memory of victims.
All London MPs, council leaders and Assembly members were invited to the event, which took place as Corbyn hosted a meeting on the same topic in Westminster.
Corbyn said: "Labour's approach to dealing with the sharp rise in violent crime will be shaped by those with first-hand experiences of working on the front line.
"Ending damaging Tory cuts to police numbers and putting more officers on our streets is essential but only one part of the solution.
"We must also learn from other initiatives that work. Glasgow has had real success in reducing knife crime by implementing an integrated approach, where the police have worked with education, health and other public services."
Speaking after the City Hall summit, the home secretary said it was "a very useful meeting" but would not be drawn on whether she accepts concerns about lack of resources.
Khan said the gathering showed the commitment of members of all parties to come together to tackle the problem.