As I predicted here last year:
>>...I'm sure you will see alcohol testing the U.K. after the recent glare of publicity stirs up public sentiment. Other American innovations like random drug tests and locked cockpit doors will catch up with you as well.<<
http://www.pprune.org/ubb/NonCGI/For...010276-12.html
This is indeed a legal minefield and careers are at stake. In America the emphasis is on treatment and rehabilitation rather than punishment. We've been doing random aircrew testing for years, it's pretty much a nonevent from my experience. The safeguards seem to work and I do think we all are less likely to abuse alcohol or drugs than before.
Here's a good FAQ on breath alcohol testing in the U.S.:
http://www.aviationmedicine.com/DOTetohtest.htm