The overriding rule here use to be keep to the left unless overtaking or turning because we drive right hand drive vehicles, this allows emergency vehicles safe and unhindered travel in an emergency and results in free flowing traffic.
When i first got my licence 50? years ago failing to keep to the left would result in loss of licence. These days it seems that no one gets taught to actually drive a car, they get taught how to get a licence and no one has a clue about how to read the road. Road curtesy is unknown and they wonder why road rage is on the rise!
Don't start me on people driving 20 Klm's under the posted speed limit on single carriage way roads with double lines so no one can pass, only to have them speed up when you can pass!
I find it strange that you can not pass on the left of a vehicle travelling in the right lane/lanes of a multi lane highway, over here they probably wouldn't know you were there in the first place. Does that rule apply in multi lane city traffic?