Police tracked a driver for more than 30 miles before stopping a car and seizing a knuckle duster from a vehicle.
The Essex Police Operation Support Group tweeted that the team arrested someone on suspicion of possession of an offensive weapon and drug driving.
They had tailed a car from Brentwood to Colchester - a 36-mile journey - before asking the driver to stop.
They said the driver tested positive for cocaine at the roadside.
The EssexOSG Twitter account said: “In addition to the warrants we still managed proactive policing. Tracked and car form Brentwood to Colchester, then stopped.
“Stop and search carried out, knuckle duster found, driver tested positive for cocaine, arrested for both.”
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