The incident happened on Watling Street, near the junction with Meadow Way, shortly after 6.50pm on Saturday 10 July 2021.
The pedestrian, a girl aged ten, was taken to a London hospital following the collision involving a yellow Audi S1. She remains in a critical condition.
A man in his 50’s was arrested at the scene and remains in police custody.
Anyone who witnessed the incident, saw the pedestrian or vehicle prior to the incident, or anyone who has any dashcam, doorbell or CCTV is asked to contact the Serious Collision Investigation Unit on 01622 798538 quoting reference HW/LB/60/21. You can also email firstname.lastname@example.org.