People are being advised to avoid a section of the M25 this weekend due to an emergency services exercise.
It will be closed to all traffic in both directions between junction 25 (A10/Enfield) and junction 27 (M11) between 10pm tonight and 6am tomorrow.
Both carriageways will be closed in order to carry out routine testing on systems and equipment in the Bell Common Tunnel near Epping and the Holmesdale Tunnel near Enfield, led by Highways England.
Using the existing road closure, a critical incident exercise will be conducted by the emergency services.
This exercise is designed to test emergency services response to a serious collision that blocks the M25 and involves emergency services from London, Essex and Hertfordshire.