Left hand is the "default" circuit direction - Rules of the Air state that all turns in the circuit will be left hand unless ground signals (and/or, presumably, the A/G, AFISO, ATSU) indicate otherwise.
At some airfields though fixed wing and rotary have different circuit directions, so be aware!
However, if you are told Runway XX that MEANS left hand circuit!!
It they say Runway XX Right Hand Circuit that means Right Hand.