Most advocates who deal with drink-driving offences will know of DPP v Moore (2003) 6 VR 430, where the Court of Appeal held the then public-policy discretion, or the unfairness discretion, could be used to exclude a result of a breathalyser test if the accused person was talked out of or denied a subsequent blood test.
The case crops up fairly frequently, but defences relying on it are not often successful.
Douglas v Police  SASC 50 demonstrates why the Moore's defence has a role to play.
The police stopped Mr Douglas and he was breath tested, returning a blood-alcohol result of 0.098% at 10:20 PM.
At 12:30 AM — nearly 3 hours later — he took a blood test, later analysed and returning a result of 0.034%.
These results indicated he eliminated about 0.027% alcohol per hour. An expert testified that 95% of social drinkers eliminated somewhere between 0.015 and 0.017%.
Expert evidence established that Mr Douglas' breath test reading probably should have been 0.06%, based on his drinking on the night and assuming he was a healthy social drinker who would eliminate around 0.016% per hour.
That suggested that the breath test result of 0.098% was probably exaggerated. The Supreme Court quashed Mr Douglas' conviction.
The result here would be different though.
In South Australia, Road Traffic Act 1961 s 47K provides that a breathalyser reading is presumed to be correct in the absence of evidence to the contrary. (See here for our earlier post on evidence to the contrary.)
Here, Road Safety Act 1986 s 48(1A) in combination with s 49(4) and (6) significantly limits when a breathalyser reading can be challenged for exceeding prescribed concetration of alcohol offences contrary to s 49(1)(f). for that reason, the points raised in Douglas can't apply under the statute but might strengthen the argument for applying the unfairness discretion (now found in Evidence Act 2008 s 135) applied in DPP v Moore.