The first incident occurred when a silver BMW collided with the central reservation barrier between junction 3 for Lightwater and junction 2 for Thorpe, and came to a stop in the second lane.
Shortly afterwards a second vehicle, a dark blue Audi A5 Sport Quattro, collided with the BMW. The force of the second collision caused the engine and gearbox of the BMW to eject from the car.
A man in his mid forties who had stopped to assist the driver of the BMW was standing on the hard shoulder at the time and received life changing injuries after being struck by parts from the vehicle.
Emergency services attended the scene and the injured man was taken by ambulance to St. George’s Hospital for further treatment where he remains in a serious condition.
The driver of the silver BMW was not injured during the collision and the driver of the dark blue Audi received only minor injuries.
The motorway was closed at junction 3 at 00:21 hours and the slip road was closed at 00.36 hours. All raods were re-opened just before 4.30am today (Monday, 6 January).
Officers are appealing for anyone who may have witnessed the collision, or saw the events leading up to it, to come forward.
Anyone with information is asked to call Surrey Police Collision Investigation Unit on 101 quoting P14004550.