Vehicle with excellent emperor carrying British cop abroad (10)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

CAR (vehicle) + AI (A1 = excellent) + NERO (Roman emperor), containing (carrying) B (British). A police officer (or border guard, customs officer etc) in Spanish-speaking countries. I’m more familiar with the Italian equivalent, but that’s spelt with an extra I before the E.