What happens when you report a drunk driver?

Hi everyone. I'm wondering if you could give me some advice. I've not long moved to the UK from Ireland so I'm not sure how it works here, but I think I need to report a co-worker for drink driving and obviously I don't want to be outed as the person who's done so. My local police website does not have an option to report anonymously so I considered using Crimestoppers, but I've read that that is unlikely to amount to anything being done.

I don't like to be that person, but this fella is out of control: he's drunk at work almost daily, he stinks of drink and can barely string a sentence together or walk in a straight line. He's currently got a huge bruise on his forearm which looks as if it has been caused by going into the steering wheel and bracing himself. His car is a mess with dings and duct tape and I'm amazed he hasn't been sacked, let alone pulled over.

Please could you give me some advice? I don't want to make enemies here at my new city, but I believe it is only a matter of time before he injuries or kills someone.