The BMA's resistance to random testing of doctors is scandalous and no doubt will be over-ruled soon. We will never know how many have died under the knife of an intoxicated surgeon or as a result of a physician's drug-clouded mind. Doctors don't like admitting errors, even in court long after the event, by which time evidence of substance abuse has vanished. If you're too drunk or doped to drive, or drive a train, you shouldn't be operating - nor working a crane or cement mixer for that matter. Nor should you be defending someone in court nor making huge financial decisions on which other people's future will depend.
Testing is cheap.
Breathalysers cost 40 with virtually no running costs while 30 urine tests for drugs only have to be carried out on a few to be effective. That means each worker is checked on average once every twenty years. Hardly a mass invasion of privacy, yet more than enough to be a powerful deterrent. This is a method that works. However random testing is barbaric unless introduced sensitively as part of a comprehensive package of education and access to confidential treatment.