The Wrong Arm of the Law (1963)

"Meet the Mastermind Who Pulls the Strings in the Underworld...and all his mobs and dolls...filling the London fog with laughter and lunacy!!!"

The crooks in London know how it works. No one carries guns and no one resists the police. Then a new gang appears that go one better. They dress as police and steal from the crooks. This upsets the natural order of the police/criminal relationship and the police and the crooks join forces to catch the IPOs (Impersonating Police Officers), including an armoured car robbery in which the police must help the gangs to set a trap.