They take impersonating Police Officers very seriously, if he was a fake and you happened to be vulnerable & he took a shine to you, are you going to object too much if handcuffed and put into a car?
Yes. If he'd tried something like this (especially for the non-incident that he was complaining about) I'd have been cycling away and calling 999 to express my concerns over a fake officer. Once someone has got out of their car (and you keep at a reasonable distance) it's dead easy to just cycle away in the opposite direction leaving them standing in the middle of the road with their car facing the wrong way. Take a few corners and you're out of the situation.
If I'd had more identifying information then I'd have loved to report it, but as it happened I had none, and I also had somewhere to be. Not much that can be done unfortunately.