The raid on four cars on the M11 took place yesterday morning near Harlow in Essex after a lengthy investigation by the Metropolitan Police's Flying Squad and Norfolk Constabulary.
The police said that no shots were fired and no one was injured in the incident which closed the southbound carriageway of the M11 over a four- mile stretch between its junction with the M25 and the Harlow turn-off.
An eyewitness said he saw bullet holes marked with white tape on a black Mercedes car. The motorway was still reduced to a single lane three hours after the incident.
A spokeswoman from the Metropolitan Police said: "We believe we have thwarted a major armed robbery planned for Norwich." The arrested men, who were being held in custody, were believed to have come from north London.