One of our members phoned 101 the Police Non-Emergency number last week, to report a speeding car. What happened next surprised even this seasoned cycle-campaigner: the operator asked whether there was any helmet-camera footage available! The 101 operators have been encouraged by the Traffic section to ask for video evidence, because it can be used as evidence!
So don't be fobbed off. If you've seen something dangerous, report it. And if you've got camera footage, the police should be interested in it.