There are long delays on the M25 anti-clockwise in Hertfordshire and Essex due to a spillage of animal waste in the Holmesdale Tunnel between J26 (Waltham Abbey) and J25 (Cheshunt).
Thames Valley Police and Highways England Traffic Officers are on scene and will require specialist clean-up crews.
Lanes 2, 3 and 4 are currently closed with motorists able to pass the scene in lane 1. Currently there are approx. 5 miles of congestion back towards Junction 27 which is expected to add at least 1 hour onto usual travel times.