They drive on the right in europe. So it's just Britain. And Australia. I'm not sure why they kept it up, but I know there's this old tradition of knights riding on the left so their swords aren't pointing at people. All horsey things are done from the left, also mostly because you carry your weapon on the left leg.
As for measurements, they use a mixture of the metric and their older systems. Metric is more professional, i suppose. People are just set in their ways.