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I belive so yes. The legislation only gives, as I recall a power to require a first screening test, then if that provides evidence of the offence or is refused the power to arrest. It would therefore follow that they have the calibrated equiptment. I know that there are available ones used for the Road Traffic Act that give a numbered read out rather than the traffic light system, these would be usable in the case of this legislation.
Koi, the police do have the option not to arrest, the legislation says 'A Constable may arrest........' not must. As to whether its a nice job or not, it can be yes, but arresting someone before they cream a bus/train/car/plane load of people accross the countryside is better than dealing with the aftermath.