the point of my post was that the problem of drug/alcohol abuse is far more widespread than people realise(James Hewitt for example).
IF B.A were to adopt a surprise tactic for drug/alcohol testing then the likely result would be rather unpalatable for the airline due to the rather large number of staff that they would have to remove overnight.
My intention is not to attack individual groups but to point out that society as a whole (and I assume that even professional aviators cannot exclude themselves from this)is not as nice as some would like to think.
Ducks for cover.