According to the British Embassy, IDPs are not required to drive a car in the UK. As long as you have a valid drivers license from your home country, you may drive vehicles up to 7.5 tons.
Though an IDP is not obligatory to drive in the UK, you may want to avoid possible hassles, especially if your license is printed in a language other than English, and buy an IDP before leaving your home country anyway. It should be carried with your regular drivers license.
You must be at least 18 years old to apply for an IDP, and they are valid for one year only.
AAA (American Automobile Association) is the only authorized provider of International Driving Permits in the United States. Currently, they cost $15.
IDP or not, you will have to get used to driving on the left side of the road in the UK. The origin of this law is because it simply made sense for feudal, violent societies where most people were right-handed: you wanted to make sure that your protective sword arm was between yourself and the other guy!
