There are severe delays on a number of routes including the M25 this evening (April 4).

It is due to a police incident at junction 23 for the motorway in South Mimms.

Update: Man arrested after serious M25 'assault'

Hertfordshire Constabulary says it was called to reports that a man had been assaulted on the M25 slip road shortly after 3.30pm.

Officers and paramedics are currently in attendance, police say, and an air ambulance has been called for the injured motorist. 

Police said at 5.30pm that this means the full carriageway will be temporarily closed to allow the helicopter to land.

The slip road also remains closed while enquiries are carried out to establish the circumstances around the incident.

As a result of the incident, clockwise traffic has been most heavily disrupted with queues tailing back towards junction 21 for the M1 near Bricket Wood, Google Maps data at 4.45pm shows.

Bignells Corner, which is the roundabout where the M25 and A1 meet, appears to be completely gridlocked, which is causing delays in both directions on the A1 at junction 23 for the M25.

As a result of the problems on the M25, roads in Potters Bar are busier than usual and traffic is heavier too in the London Colney area.