niknak
Maybe the difference is that we have a fully documented and controlled procedure using independent agencies to undertake the drug and alcohol screening.
All these procedures were implemented with the co-operation and agreement of the relevant railway Trade Unions.
In the Railways, and similar to yourselves no doubt, we do not as a matter of routine summon the Police if we believe (for example) that someone may be under the influence.
We arrange for them to be immediately relieved of duty, isolated with somebody, and 'For Cause' screened.
In all circumstances when a person is 'Post Incident', or 'For Cause' screened they are also by procedure immediately suspended from duty pending the outcome.
It is not normal practice to involve the Police in such cases.
If the Police attend an incident they can choose to exercise their right to require a person to undergo screening.
It appears strange that your organisation does not see fit to prohibit reporting for duty under the influence??