and would you ?
Takes a lot for me to say "***'in ell" but I did !!!!
I know the system at my local StageCoach branch having had a few run ins over the last few years.
If you feel strongly enough, I would contact your local Police and quote the crime number at StageCoach. If you don't feel that strongly, then maybe its not worth complaining about ? (actually, one for the psychologists: I have noticed that victims go from hopping mad anger about somebody risking their life, to denial afterwards not wanting to make a fuss and so don't complain).
Next up, it is worth making sure you are contacting the right depot. Cambridge, for example, has buses run from more than one depot. You will be forwarded to the right one but it may introduce delays.
You need evidence ? On the modern SC buses, they are now equipped with CCTV facing in and out, possibly 10 cameras. Tell StageCoach to save the footage of you and say you are making a "Subject Access Request, under the terms of the Data Protection Act". You shouldn't need to say that but it helps. The Police won't know about the DPA, and StageCoach will try to fob you off. If they have recorded you, you can ask to see it and have a copy. Don't get your hopes up about quality, it is actually about 1FPS, but might be enough to prove speed and distance of the pass. If you want to see the footage yourself, and not just trust a Police Officer, SC will have to go to a lot of effort to blank other identifiable people out of frames. One frame might be all you need though.
In a serious incident I once failed to get footage because I did not know the system and it was overwritten automatically after 5 days. SC were in breach of the Data Protection Act here, being unable to provide the footage.
I have got as far as getting a frame from a not quite so serious incident involving my son, which I decided to take no further.
If you did want to take it further and you have evidence, then you are in the hands of the Police. And, from the stories on CycleChat, I suspect without a collision it will be very hard to get a result. In my mind 3 points on the licence is justice. Having said that, I think being a persistent complainer has paid off. I rarely get trouble from SC now. Maybe word spread around the depot about the PITA on Route 8 out of Cambridge :-)