A woman was followed and approached by a man in a car with a blue flashing light on top in East Harling, Norfolk Police has confirmed.
The police said they received a call on 7.15pm on Friday following concerns from a woman who stopped for the car.
Should anyone get stopped they should unwind their window a little and ask to see the officer warrant card - they can then dial 101 to confirm identity
The male driver left the vehicle, and asked the woman to step out of her car. She declined, but said she was happy for the car to follow her to a well-lit area.
But as she drove into East Harling, the driver of the suspicious vehicle drove off.
Police say they have no lines of enquiry but the car has been described as small and dark in colour.
A spokesperson for the police said: “The female driver has been offered reassurance and advice that should she see the car again to call the police.
“Should anyone get stopped they should unwind their window a little and ask to see the officer warrant card they can then dial 101 to confirm identity.”