The fire service is at the scene.
The plans include moving a veterinary facility from London to the Southridge Animal Centre.
The campaigners say vulnerable people are housed in HMOs and they attract anti-social behaviour.
Henri Nikolli, 19, from Welwyn Garden City, is jailed for multiple drugs and firearms offences.
The cast say they made friends for life during the filming of the new BBC One series.
Specialist contractors are sent to the scene to clear a "significant oil spillage".
Passengers are being advised to check before they travel as major engineering work takes place.
National Highways says there are delays of up to 30 minutes in the area.
All lanes are reopened at about 07:00 BST
