I don't think breathe or Blood/Alcohol testing is a problem (although there is evidence to show that breathe testing does not accurately reflect blood/alcohol), apart from the relatively low "zero tolerance" levels set (as there are no easy guidlines apart from complete abstinence).
Saliva and blood testing are the most reliable methods.
Despite the fact that the legislation and the CAA both mention urine testing, I find this odd (not that the CAA have helped much).
Urine testing does not reflect impairment. Although commonly used for (non-traffic) drug testing, it is not generally used in court for prosecution - as it does not provide proof that you were "under the influence" at the time of arrest.
Hence it is possible for a person to be clear in both breathe and blood tests, but for their urine test to be positive. I think that urine testing is unlikely to be used in court.
As for drugs, well don't hold your breathe! (pun intended)