Officers are appealing for witnesses to a serious collision near Junction 4 on the Londonbound M2.
Two vehicles, a black Citroen Berlingo van and a gold Volvo estate car, collided at around 2.30pm on Saturday 18 May 2019 within the site of the Medway Services.
An unmarked police car, which was in the vicinity and had been travelling behind one of the vehicles earlier, initially attended the scene and was joined by colleagues from the Serious Collision Investigation Unit and teams from the Kent Fire and Rescue Service and the South East Coast Ambulance Service.
The driver of the van sustained injuries and was taken to a London hospital via air ambulance where he remains in a serious condition. A second man was taken to a local hospital as a precaution.
A man and a woman were arrested in connection with the collision and remain in police custody.
Kent Police has referred the matter to the Independent Office for Police Conduct due to the proximity of the unmarked police vehicle.
Investigating officers would like to speak to anyone who was at Medway Services or in the surrounding area at the time of the collision and witnessed it, or has dashcam footage.
Witnesses are asked to call the Serious Collision Investigation Unit appeal line on 01622 798 538 or email [email protected] quoting 18-903.