Vauxhall Corsa - Pls help! Rear ended a car that suddenly stopped

I was driving down A494, at the back of a white BMW X5. We were proceeding down a slope when I saw the BMW stop, and then signal to turn right after a traffic light, which was green at that time. So I quickly hit the brake pedal and slowed down and then he started to move off. Then, the BMW braked unexpectedly at the middle of the road and I jammed my brakes too, but it was too late. Before we had time to react to the shock or even take down his car plate number, he drove off. I drove into a side road to assess the damage done to the car. The car’s bonnet was bent, and one of the headlights was gone. We were parked at the side of a bar, and the bar owners kindly allowed us to borrow their telephone to call AA. The bar owners also directed us to their car park to wait for assistance. About twenty minutes to half an hour later, a man who was on the phone came towards our car. He was saying something like “the other car tried to flee the scene”. At first, we didn’t know that he was the owner of the BMW, and thought that he was calling for our benefit. I asked if he was the driver of the BMW, he told us that his wife was the driver only after I asked him many times. He turned out to be calling the police, telling them that we were trying to run away. He also told the police that his wife was traumatized by the crash. I asked him why the car stopped there suddenly, and he just retorted that the brake lights were on. After a while, he left to drive the white BMW back to the car park, alone. We saw that the damage done to his car was not as great as ours; it was just a dent to his rear bumper. He then parked the white BMW then approached us again warning us not to try to escape and to be prepared to pay for the reparation fee on his “expensive car”. After that, he left again, coming back with another car this time, a light blue BMW, with his wife. They then entered the bar nearby. Before the arrival of the police car, a lady, his wife came out alone from the bar for a few times while we were waiting in the car. When the policeman came, I tried to tell him about what had actually happened but he couldn’t be bothered to listen to us and just told us that it is the fault of the rear driver no matter what, which is indeed the law. Besides, the policeman insisted I exceeded the speed limit of 30mph yet I am pretty sure I did keep my car speed below the speed limit mentioned, as I slowed down at the slope. What was puzzling was that the car drove off right after the impact, without stopping to assess the damages, and only came back such a long time later. When we received his details from the policeman, we realized that his address was just a two minute drive away from the site of the crash, which makes it all the more perplexing. Furthermore, when they were driving off from the car park, the supposedly traumatized lady driver smiled and waved at us. Also, when we took another look at the road, we realized that it was actually possible for a car to pass when another was taking a right turn, as that was the driver’s original intention to do so. Instead of turning, he jammed his brakes suddenly that was when we drove into him. Would we have a case if we made a separate police report? All help would be appreciated!