If for example, someone comes to the services having driven, after drinking a small bottle of vodka, it might seem ok to give them something to eat say, ask them to stay to group, breathalyse them and if they are under the legal limit by then, let them drive home. The best thing to do however is ask for their keys, tell them to get a taxi home and come back tomorrow for their car. Say that you will report them to the police if they leave and drive off, and do this if they leave and drive off. Perhaps your breathalyser test was wrong, or they really aren’t able to drive, it is always best to be cautious.