Why do the English drive on the left?

There is a logic that has evolved since olden days about keeping to the left on the road. 

In olden days people wanted to protect themselves using their sword while they were passing each other on the road. To accomplish this they had to be in the best possible position to use their sword in order to protect themselves. Since most people were right handed, they felt it convenient to keep to the left and use the sword in their right hand. 

A common question that arises is why people drive on the right in other parts of Europe. It is believed that the reason behind this is Napoleon, who after conquering Europe, fixed the major roads and established traffic on the right side. Some believe that he did so to go against the way British travelled, while others believe that it was easier for him to control the horse with his right hand, and hence he made everybody else travel on the same side as he travelled.