I think we need to keep in mind that it's deemed to be suspicion, and suspicion is a very low threshold and suspicion is what is needed to move to the screening stage at the roadside, which is simply to ask for a sample of breath on the approved screening device. It is only if the individual driver fails on the approved screening device that they will be taken to the police station, given their right to counsel and then receive a demand from the police to provide samples on an approved instrument, and the approved instrument gives the actual readings that would be used in court.
On October 18th, 2016. See this statement in context.