As you know, custodial sentences depend on many factors but if the alleged drug dealer is caught bang to rights it may at least interrupt their activities until their case is dealt with - and this may be all that is needed for your relative to stop their recreational use of cocaine.
Please read this from Crimestoppers website:
"What we mean by anonymous
Anonymous means that your name is not known or made public.
We will never ask for your name
Your call will not be recorded
Your call or online form will not be traced
You will not have to make a statement to the police
You will not appear in court
We know that our guarantee to never ask for your name or record your call is vitally important to you.
It makes it easier for you to come forward, breaking the silence around criminal activity and removing your fear.
Crimestoppers' guarantee of anonymity has never been broken"
Vist the website at www.crimestoppers-uk.org and make the call or report online.
There's no guarantee that anything will happen in the near future, but at least you will know that you have done what you can at the present time to help your relative break a dangerous habit.