A female pedestrian walking along the motorway just before 3am on Sunday near Staines Junction 13 was hit by a vehicle and has died.
The woman, who was in her 30s, was pronounced dead at the scene.
The male driver of a black Volkswagen Golf, which was found nearby, has been arrested on suspicion of failing to stop following an injury road traffic collision and providing a positive breath test. He remains in custody and will be interviewed later today.
Shortly after the fatal collision, a second collision took place between Junctions 13 and 14 of the M25.
An officer in a police vehicle had put traffic control measures in place in response to the fatal collision when the second collision, involving a white minibus, a black Range Rover, a silver Vauxhall Meriva and a bronze Honda CRV, took place.
The driver of the minibus, who was the sole occupant of the vehicle, was taken to St George's Hospital in Tooting with a serious leg injury and is expected to undergo surgery later today. The driver of the Range Rover was taken to St Peter's Hospital in Chertsey with a suspected neck injury. The occupants of the other vehicles involved escaped uninjured but were treated at the scene for shock.
The M25 was closed for several hours anti-clockwise from Junction 14 at Heathrow Airport to Junction 12 at Chertsey while emergency services dealt with both incidents but has since been reopened.
Police are appealing for anyone who saw the female pedestrian walking in the area or along the motorway prior to the collision, or anyone who witnessed either of the collisions, to contact the Collision Investigation Unit straightaway on 01483 639922, quoting incident reference P15008681.
