If you suspect someone’s drunk when driving - is there much point in reporting?

I’ve thought that a few drivers are over the limit during my time but never reported one (assuming 999?) have always thought it’d be too late before the police get to them and so on.

If you have reported anyone is there much of a process? Do you get feedback/confirmation?

Before this gets misconstrued I’d definitely be keen to report unsafe/suspected drunk drivers just want to know others experience with the system and process of doing so.