following obviously drunk driver- what to do?

[alecrain]

Just today, driving east on M1 (in the 80km/h zone -roadworks) I was tailgated by a Statesman, he was very close behind me and I noticed that the car wasn't going in a straight line. Moments later roadworks ended so I sped up to 100km/h to get away and he sped up and overtook me on the left (doing at least 120-130) and wasn't using his indicators properly then got stuck just in front of me and tailgated another driver, still driving in a slight zigzag, sometimes crossing the lines.

I followed him till he exited the freeway.

Now, what do you do in those situations?

Can you call the police and follow him until they catch him?
Do you just call them afterwards and give them the details?
Do you just assume that he didn't have wheels properly aligned- thus not driving straight?

Has anyone had a similar experience?