A 23-year-old man died when the vehicle he was in crashed in Buckinghamshire while it was being followed by police.
Police said officers followed the car in High Wycombe after it made off when a patrol tried to alert the 20-year-old driver that his lights were not on.
The VW Bora was seen in London Road, Loudwater at about 0200 BST on Saturday and left the road after travelling about half a mile, police said.
The driver was airlifted to hospital with serious injuries.
The incident was referred to the Independent Police Complaints Commission and they decided it could be investigated by the Thames Valley force.