Just before 6.30pm, officers were called to a report of a multi-vehicle collision involving a blue Bugatti and an ambulance on blue lights, on the northbound carriageway of the A6, near the Barton Road junction.
A man in his 50s was pronounced dead at the scene.
His next of kin have been informed and are being supported by specially trained officers.
Sergeant Tim Davies, from the Bedfordshire, Cambridgeshire and Hertfordshire Road Policing Unit, said: “Our thoughts are with the family and friends of the victim at this time.
“I would urge anyone to contact us as soon as possible if you witnessed the collision or were driving along the A6 at that time and saw the incident, especially if you have a dash cam fitted to your vehicle.”
You can report any information to Bedfordshire Police, including video footage, via www.beds.police.uk, quoting Operation Fortress.