doctor's jeep green light on roof flashing up the M1

What the story on doctor cars and lights. Traffic was heavy coming up the m1 just now. Behind me I could see flashing lights . It was the on call doctor car. It was doing the speed limit. I pulled over and left it go on. But as we past the m1 apple garage. There was a garda check point on the slip road into the garage. Here the thing is the doctor car switched off its over head flashing lights and went into the left lane of m1. Once past the junction all the flashing lights came back on. Are they allowed run with lights on up the road. Just wondering is all. Thought only the fire ambulance and garda could do this.