There are seven miles of tailbacks on the M1 southbound after the smash near junction 15a for Northampton. Highways England cameras show bumper-to-bumper jams past junction 16 for Weedon Bec and Upper Heyford.

       All lanes were shut but one reopened at around 1.45pm. Highways England has warned drivers to expect an additional 45 minutes on journey times.

       Traffic is also busy on alternative routes, such as the A5 through Weedon Bec and Stowehill, and the A4500 in and around Northampton itself.

       The M1 northbound is slow on the same stretch due to onlookers.

       Authorities say tailbacks are past junction 15 for Northampton south and Roade.

       It is unclear if anyone is injured in the accident and, if so, to what extent.

       "We are currently working to release the trapped traffic and get a further lane back," a Highways England spokesperson has said.

       "As soon as this happens, we'll update our feed. But we have no ETA at this time."