A 34-year-old woman was taken to Kings College Hospital in London with head and internal injuries after the Ford Fiesta that she was driving was in collision with a white unmarked Surrey Police Transit van on Friday (28 June) on the A29 at Warnham, near Horsham.
Emergency services including West Sussex Fire and Rescue, arrived at the scene at around 1pm.
A spokesperson for Sussex Police said: “The injured woman remains in hospital in a critical but stable condition. The driver of the van was taken to hospital suffering from shock and minor injuries.
“The road was closed for over four hours whilst collision investigators examined the scene and police would like to thank drivers for their patience.
“If you witnessed the collision please call 101 quoting Op Kirby or e-mail firstname.lastname@example.org”
The IPCC has been informed.