Not sure what priority it will take at the moment, though if the same vehicle or location gets multiple reports that’s probably picked up by the computer and routes to KCH might be on a “watchlist”, but you can report online to the Met Police [www.met.police.uk
The AA recommend having a note of
* The vehicle's registration
* The vehicle's colour, make and model
* The time and place where the incident happened
* Any other details, such as a description of the driver
The Met Police’s website asks for dashcam footage 2 minutes either side of the incident.
If you see something worrying and have time to report it then it can’t hurt and might take a dangerous driver off the roads.