A 23-year-old woman was airlifted to hospital on Christmas Day after a Leighton Buzzard driver lost control of the car they were travelling in.
The red Fiat Punto collided with trees and a metal barrier as it was sliding down the embankment after veering off Stoke Road, Linslade, at around 9.20am on Wednesday.
A road ambulance and air ambulance were dispatched to the scene and the 24-year-old female driver was taken to hospital with slight injuries.
The injured passenger is currently receiving treatment at the hospital in Cambridge after suffering from a serious head injury.
Officers from the Bedfordshire, Cambridgeshire and Hertfordshire Collision Investigation Unit have launched an investigation into the road traffic collision.
The officer in charge of the collision investigation, PC Dave Clarke, is keen to trace anyone who witnessed the collision and who has not already spoken with the police.
Anyone with information relating to this investigation can contact PC Clarke on 01438 757500 or
Bedfordshire Police on 101, or text information to 07786 200011.
Alternatively you can contact the independent crime fighting charity Crimestoppers, anonymously, on 0800 555 111.