Our cops don't even have to do that !!!
We have a truely fantastic system called ANPR (Automatic Number Plate Recognition)
Its the dogs danglies.
A traffic cop or DOT vehicle has a camera mounted on it, it focuses on the number plate and within milli seconds the PNC (Police National Computer) has a response from where all our data is stored at the DVLC (Driver, Vehicle and Licencing Centre).
They can tell ...if the vehicle is taxed (we pay a tax to drive on our roads) has a current ministry test certificate of roadworthyness and if its insured.
It also can tell them if the registered keeper has any warrants or is banned from driving. It can even flag the history of the vehicle eg if its been stopped for drugs, violence or crime related incidents.