Driving on the left side of the road

Carl and I sat at the pub last week with another couple, wondering aloud why it is that the British drive on the left side of the road. When we got home, I decided to look it up on the internet, and I found one plausible explanation.

In the very early days of travel in Great Britain, men had to protect themselves from others who might attack them on the roads. Because most men were (and still are) right handed, they travelled on the left side of the road to leave their right hands free in which to use their swords in self-defense if necessary against anyone who approached.

As I discover any other theories or explanations, I will share them with you.