A bogus policeman pulled over a car to lecture its occupants about their driving only to find the driver and passengers were genuine officers.
The real, plain-clothed officers had been travelling in an unmarked car on Saturday in the early hours.
Officers said the man forced their car to stop on the A23 near Brighton.
"After giving the officers a ticking off about their driving, the individual realised his mistake and tried to escape," a police spokeswoman said.
She said an arrest had been made in connection with the incident and that a man had been bailed for six weeks.
Officers have asked any members of the public who have been a target of a bogus policeman to contact Sussex Police.