Ok when you say smoking im going to assume you mean smoking weed, yeah it would be more respectful if they let you tell your parents yourself but would you actually tell them? and how do you think they would react to it??

The cops always take down your details just incase they need to get in contact with you again which in most cases they dont so dont worry about that.

I dont know what your friends parents are like so i cant say what they are going to do but im sure you must know them quite well, do you think they will tell your parents?, are they good friends with your parents? if you think they will then maybe you should just tell your mum and dad yourself thats my advice.

Or you could just ignore it all together... and see what happens they didnt catch you in the act did they? so you could just say that your friends were doing it and offered you some but you said no.