That was the norm at one time.There are in fact a great many countries where people drive on the left.Basically because most people are right handed.
There is strong evidence that it's safer for physiological reasons.The dominant eye is the right and in cars with manual gears the weaker arm comes off the wheel , also the case when using other controls.More than anything though is a human tendency to swerve to the left when in a panic.Whatever, in comparable countries the accident rate is well down in right hand drive countries compared to their friends who drive on the right.British road fatalities per 100 000 people are the lowest in the EU despite the traffic density.
Fron the statistics office ;
The United Kingdom has a relatively good record for road safety compared with most other EU countries. In 2000, it had the lowest road death rate in the EU, at 6.0 deaths per 100,000 population. This was also substantially lower than the rates in other G8 countries such as Japan (8.2 per 100,000 population), Australia (9.5), Canada (9.7), and the USA (15.2)
Fatalities in the UK have fallen since 2000.