Reporting an incident of bad/dangerous driving, you can report it online at the time or soon after and upload a photo or video that includes the number plate details to https://www.westmercia.police.uk/police-forces/west-mercia-police/areas/west-mercia/campaigns/campaigns/2019/operation-snap/
If a road is blocked by such an incident, you need to report it at the time to 101.
Submitting data to Operation Snap requires you to give your personal details and agree to go to court if required. However, only 1-2% of reported offences actually go to a court case, in most cases a driver improvement course or fixed penalty notice will be issued.