Two men were arrested by armed police following an operation on the A1 at Peterborough last night.
Police deployed firearms units and dogs after a tip off about a black BMW which was travelling on the southbound carriageway at around 5pm.
Officers put a rolling roadblock in place to temporarily stop traffic while they apprehended two men in the vehicle and took it off the carriageway to Haddon Services.
Two men, aged 32 and 31, from Essex were arrested of suspicion of possessing a firearm with intent to cause fear of violence.
Although the operation involved Cambridgeshire Police officers it was led by Lincolnshire Police and has now been passed on to Nottinghamshire Police to investigate.
Both men have since been released under investigation while enquiries continue.