PC Martin Willis, of West Yorkshire Police, shared the shocking dash cam video on Twitter after the driver's sudden stop led to an hair-raising near miss on the M621 in Leeds.
He had been responding to an emergency call on the M621, an eight-mile loop of motorway that takes traffic into central Leeds between the M1 and M62 motorways.
The officer had activated his flashing blue lights and siren before picking up speed and overtaking passing traffic.
He had passed a number of cars without incident before a car suddenly stopped in the outside lane - just metres in front of his patrol car.
PC Willis immediately applied his emergency brake and narrowly avoided a nasty collision with the car in front.
With both vehicles at a complete stop in an outside live lane, PC Willis had no option but to stay at the scene to protect the now vulnerable car from other traffic.
He said: "Leaving a vehicle stationary in the outside lane of a motorway with no rear protection and with vehicles bearing down on it would have put the driver and his passengers at risk of being hit.
"This meant losing precious time in responding to an emergency call.
"I had to go and speak to the driver and give him instructions on how to move off and then escort him to the hard shoulder.
"He stated that he thought I was wanting him to stop.
"This is not helpful. If you see blue lights behind you, please move over. If the emergency vehicle is going to a job, it will pass you.
"If it wants to stop you, it will follow you onto the hard shoulder.
"NEVER stop in a live lane!"
He added: "Apologies for having no audio in the video, but as you can imagine, it was unbroadcastable!
Garry Wilson, a former instructor in Emergency Response Driver Training, said there needs to be more training for drivers in how to respond to the presence of an emergency vehicle.
He said: "As a previous blue light instructor we try to educate our drivers to look in the far distance and plan as much as possible.
"But there is always going to be those unexpected and challenging situations where you need to stay calm and focussed.
"I think more training is needed for the public on how to deal with situations like this, especially on motorways."