The low level of the alcohol limits (0.02% blood/alcohol) has interesting consequences. The breathe or saliva test on its own is not currently sufficient evidence to convict - so corrobating evidence in the form of a blood test is necessary.
The body metabolises alcohol quite rapidly.
If a pilot were tested positive at or near this 0.02% limit, then it is probable that they would pass a blood test taken later at the police station. This is because it would take some time (perhaps an hour or so: arrest, read rights, transport etc.) to administer the blood test which has to be carried out by a Doctor, during which time the remaining alcohol would almost certainly have been metabolised by the body. (Urine tests are irrelevant as they do not indicate intoxication). Hence I think the alcohol limits are "evidentially suspect" (back calculation of alcohol levels not being legally acceptable).
As I have noted before, "drugs" are also included in the legislation, but no indication is given as to what a "drug" is or what the "blood drug" cutoff levels are. Presumably, they will be set at the "zero tolerance" level. Providing an acceptable "zero tolerance" drug test regime for courtroom purposes may be difficult (some drugs metabolise quickly, whilst others can be present for days or even weeks). This may be an even more serious issue.
In addition to all this, individuals are entitled to have recourse to testing for Defence purposes. Yet there seems to be no effective means for this at all (other than for blood/alcohol testing).