The 44-year-old woman from Northampton was driving east bound on the M4 and exited at Junction 13. At the roundabout she became aware of a grey car with foreign number plates alongside her.

Two women got out, shouted abuse and then kicked and punched her before getting back into their car and driving off.

With a cut face and mouth, and a slipped disc, an ambulance took her to Royal Berkshire Hospital, and she may yet need surgery.

The two women were white and aged in their early twenties. One had frizzy blonde hair and the other shoulder-length brown hair. The car was possibly a Peugeot and had a registration beginning ZZ. There was another woman sat in the back of the car.

PC Gareth Miles of West Berkshire police said: “These women acted in a very violent way and I need to trace them. The assault happened at a busy time of night and they were in a very distinctive car, so I hope someone will be able to help and will get in touch.”

Any driver who has information on the car, its occupants or any part of the incident is urged to contact PC Miles via the Police Enquiry Centre, on 0845 8 505 505.