If you go here:
http://travel.state.gov/visa/temp/wi...hout_1990.html
you will see the regulations for travelers coming from a "visa waiver" country such as UK.
I agree with the suggestion of "patience". Depends on the mood of the guy in the booth. You very likely will have to go into the office at the crossing point. It should be "yes, sir", "no, sir", and "Thank you, sir". Muttering about the lineage of the agent should only be done in the car at least 100 yards later.