Road Policing Officers pulled the vehicle over while on patrol in the Capital on Saturday evening (July 2).
The driver of the vehicle allegedly had cannabis in their possession and tested positive for the Class B drug on a DrugWipe.
During a search of the vehicle, officers also say they found the large serrated knife and balaclava.
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Police arrested the individual, whose blood was taken for further testing.
Enquires are ongoing regarding the knife.