The UK and the US have different governments, indeed different systems of government, and there is no reason for anything to be the same in the two countries. It is true that public use aircraft are not regulated by the FAA, and their pilots are not required to be licensed by it. That's the law here, like it or not. Most agencies require an FAA license, and maintain their aircraft in accordance with FAA practices, and the aircraft mostly have a standard airworthiness certificate. But none of this is required by law, and not all agencies abide by all, or indeed any, of these things. Surplus military aircraft are common in police agencies, and cost-cutting is not that unusual. If this frightens you, then by all means stay across the pond.