This police car dash cam footage shows a foolish driver slam on his brakes and stop in a motorway fast lane - blocking the way of an officer rushing to an emergency.
PC Martin Willis, of West Yorkshire Police, was tearing along the M621 in Leeds after receiving reports that members of the public were walking on the carriageway.
The 54 second video shows responsible road-users moving to the left hand lane to make way for the emergency vehicle, which had both its sirens and lights on.
But then a BMW in the fast lane can be seen slamming on his brakes and coming to a complete standstill on the road - forcing PC Willis to carry out an emergency stop.
The officer then had no choice but to remain in position in order to protect the driver in front, who had placed himself in danger as a result of the stoppage.
PC Willis approached the motorist, who said he had stopped because he thought the police car was trying to pull him over.
The traffic cop explained the dangers of blocking a live lane before sending the red-faced driver on his way.
PC Willis 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."
He added: "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."
Garry Wilson, a former emergency response driving instructor, said there needs to be more training for motorists on how to react when confronted with 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 focused.
"I think more training is needed for the public on how to deal with situations like this, especially on motorways."