Returning to Duggan, I know nothing of gang culture but I doubt that you claw your way to the top in the gang world by being nice to people.
Jim described him as a "petty criminal."
The Met Police do not call out armed response units to support the arrest of petty criminals.
Only dangerous criminals.
And, they would never choose to make the arrest while the suspect was inside a moving vehicle, on a busy street during the rush hour!

This would only be done as an emergency measure to prevent an even more serious incident.