Last night I was driving home through a national park. It's a 60mph limit road but was very dark, (unlit road), the road service isn't great and the white lines are patchy and faded. There are also lots of deer about and there are often crashes, so I was going at 50 miles an hour.
One car passed me at about 63/64mph and then shortly afterwards a car came from nowhere, and overtook me way faster; a car has never overtaken me so fast on a 60mph road before. He flew past both me the car in front of me (that was still doing 63/64mph from overtaking me). He then cut in front of that car because there was something coming the other way. The speed in which he was going was so fast that it actually made me gasp and my hand flew to my mouth - and I am not a gasper. 
. His numberplate was obscured at the back so I couldn't tell what it was and he was going so fast that you couldn't see anything much else except that it was a black saloon.
About 15 minutes later on the same road everything came to a stop. Local news reports have reported that not only was there a multi car crash, but there was also a separate incident whereby a car was burnt out in a layby on the same road very close by.
My dilemma is: do I do anything? Do I ring the police? What can I tell them if I do that's of any use? The only thing I can tell them is that a car drove past me extremely fast and dangerously but that I don't have a number plate, I don't have the car type, or see the driver or occupants. Nor do I know that the cars involved in the multi car crash or in the fire were the same car. It's just a coincidence and based on a strong suspicion that a car driving that dangerously would shortly be involved in a crash.
Would the police actually be interested with this information and would it ever be of any use - or shall I just leave it? I worry that this driver has hurt other people and will try and blame them for bad driving whereas, he was driving atrociously beforehand and people need to know that.