There are some right bum holes on the road!
I'd go ahead and formally report him. I once took the registration of a speeding police car (no lights or bells) and the police took it very seriously and called him in for a bollocking. They said: "your word against his", but he confessed!!!!!! I don't know what happened in the end but I felt better being able to do something about it.
It was a speed trap police Volvo that I ususally saw parked on a long straight stretch of road in the mornings.
Go ahead and report the bugger. It'll make you feel better.