Road Traffic Act 1961

a person is qualified to drive a vehicle, or to start or stop its engine, if the person—

holds a driver's licence of the appropriate class to drive the vehicle and the licence is not suspended; and

is not prevented under a law, including, for example, by the conditions of the driver's licence, from driving the vehicle at the relevant time;

a person is fit to drive a vehicle, or to start or stop its engine, if the person—

is apparently physically and mentally fit to drive the vehicle, or start or stop its engine; and

is not apparently affected by either or both of the following:

alcohol;

a drug that affects a person's ability to drive a vehicle; and

the person has not at the time been found to have, and there are not any reasonable grounds to suspect that the person has, a concentration of alcohol in the person's blood exceeding the amount permitted under a road law; and

the person has not at the time been found to have, and there are not any reasonable grounds to suspect that the person has, a prescribed drug in the person's oral fluid or blood;

a person is authorised to drive a vehicle, or to start or stop its engine, if the person is its operator or has the authority of the operator to drive it or to start or stop its engine (regardless of whether or not the person is qualified to drive the vehicle, or to start or stop its engine).