Just checked the US Embassy website and found the answer:
Will my British driver's license be adequate for renting a car?
The U.S.A. has an agreement with most countries whereby the renter's full national driving license may be used for a period of up to one year in the U.S.A. This applies to the full U.K. driving license. Provisional licenses are not acceptable.
Most car rental companies require that you have held a full license for at least one year, regardless of age. The minimum age for renting a car is normally 21 although it can be as high as 25. Often an additional charge is levied on drivers who are under 25 years of age.
International Driving Permits are generally not required in the U.S.A but it is helpful to carry one. If they are taken, they are only valid in conjunction with a full national driving license. They should not be accepted on their own. It is recommended that drivers who possess a full national license that is in script other than Roman, i.e. Cyrillic or Arabic, should also obtain an International Driving Permit (IDP).
Young drivers may wish to obtain an International Driving Permit to use as a photo ID, in place of a passport, for entry into bars and nightclubs where the minimum age for entry is 21 years.
If you have endorsements on your license, do check with your rental company that these do not present a problem.
We suggest that you check the requirements of your prospective automobile rental company by contacting them direct.
