A bomb squad was called after concerns about an unattended Vauxhall Corsa at Workington police station, Cumbria.
Roads around the building, in Hall Brow, were sealed off and an explosion carried out at 08:00 GMT.
The force blamed "an internal communications error" and apologised to the owner.
Cumbria Police said other officers on duty were not aware colleagues had parked the car outside the station after helping its owner, who had taken ill.
The building was evacuated, a 100m cordon put in place and the vehicle blown up.
Insp Ashley Bennett said: "We have made contact with the owner of the vehicle, explained the situation and have apologised to him.
"The officers who dealt with this morning's incident did so with public safety in mind and followed the appropriate procedures in respect to an unoccupied suspicious vehicle.
"The constabulary will review this incident and will take on board any learning."
A police force carried out a controlled explosion on a "suspicious" car outside a station, not realising its own officers had parked it there.