A pair of feet sticking out of a rolled-up carpet – believed to be a body – turned out to be a mannequin dressed as Prince Charming.
The suspicious object, spotted on the M11 motorway, prompted a call to Cambridgeshire Police, who were deployed to track down the car.
When they found the vehicle, they were told by the driver that he was taking the dummy to a themed birthday party.
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Cambridgeshire Police said: “When we received a call on Saturday lunchtime to reports a vehicle was travelling along the M11 with a pair of feet poking out the end of a rolled up piece of carpet, alarm bells were naturally ringing for the informant and our control room.
“We managed to track the vehicle down in Angel Drove, Ely where our officers discovered there were indeed a pair of feet… belonging to a mannequin dressed as Prince Charming who was on his way to a themed birthday.”
The force said the driver was given advice “to avoid such circumstances again”.
It added: “Thankfully this was a false alarm.”