Originally Posted by
Hyperacusis
Correct. Your IDP is worthless in the US by itself if stopped by cops. If your UK based license is in English (which it is), there is no reason to get an IDP when travelling to the US.
An IDP should always be accompanied by your national license. The AA does recommend an IDP for most non european countries including USA and Canada. One reason is for insurance purposes. If you are unfortunate to have an accident you do not want to run the risk that you are not licensed to drive in the state/ country.