Why did Nortons shift on the right?

Back when motorcycles were motorcycles, there were mostly European bikes and British bikes. Many early Japanese bikes were copies of European bikes. In Europe, they drive on the right, In the UK, they drive on the left. It makes the riders' brains different. I think a lot of continental race riders used to push-start their bikes from the right hand side and stand on the gear change with their left foot, as they stepped over. British riders pushed from the left hand side and stood on the gear change with their right foot, as they stepped over. On British public roads, it might be dangerous to push-start a bike from the right hand side. When I road-raced a Japanese two-stoke, push -starting it from the right hand side would have given me a problem, but by then all races were clutch-start.