Essex Police officers had stopped a vehicle on the M25 on December 12 to speak to a driver in connection with motoring offences.
The driver had been stopped at around midday on the M25 between Hornchurch and Brentwood, near to the junction with the A127.
Officers had required the man, aged in his 20s, to undergo a roadside drugs test. He was then arrested on suspicion of drug driving.
However, another vehicle then hit the man. He tragically died at the scene despite the best efforts of police officers and paramedics to provide life-saving care.
The section of M25 was closed for most of the day, whilst emergency services worked at the scene and conducted a thorough investigation.
Some drivers were stuck behind the incident for over three hours, before eventually being turned around by officers. The closure of the M25 caused significant tailbacks of queuing traffic throughout the day and into the evening.
Essex Police has since referred itself to the independent police watchdog over their involvement in the fatal incident.
Chief Superintendent Simon Anslow said: “Our thoughts are with the man’s family and friends at this difficult time. We have made a mandatory referral to the IOPC and it has decided to take on the investigation independently.
“We know this incident will be concerning to the public and we are being as transparent as possible at this early stage of the investigation. Our officers are witnesses to this tragic incident and are being supported.”
Any witnesses yet to speak with police are asked to call 101 reference CAD 2866/12Dec.