I think the idea behind it is great, but I have been unfortunate enough to work with soldiers who regularly do pills/cocaine without being caught. There is a very limited period of time (I forget the exact figure, but it's a few days) when this type of substance can actually be picked up using the CDT tests.
Personally I think that members of certain public services should be subject to CDT type conditions too, such the Police, Fire and Ambulance service and Nurses and Doctors. Granted this would cost a fortune but in the ideal world it should be the norm seeing as the degree of trust placed in these people is at a similar level if not higher at times to that of servicemen and woman. As for MP's are they resorting to drugs now instead of the kinky sex games that they used to participate in the 90's??