“No idea why, and it makes no sense the way they do it.”
Brits drive on the left.
Knights of old
Driving on the left side goes back to Medieval England where Knights would ride their horses on the left side of the road so if they encountered an enemy their sword hand would be on the right side.
England has never let go of this, and is still ready to sword fight to this day.
On a four-lane divided highway, the Brits call the lane closest to the median the outside lane and the lane closest to the side of the road the inside lane. We call the lane closest to the median the inside lane and the lane closest to the side of the road the outside lane. That is the difference I was referring to, and it has nothing to do with driving on the left or on the right.