Subject to paragraphs (2) and (3), a person required F1under Article 18 to provide a specimen of breath, blood or urine may afterwards be detained at a police station F2(or, if the specimen was provided otherwise than at a police station, arrested and taken to and detained at a police station) if a constable has reasonable grounds for believing that, were the person then driving or attempting to drive a mechanically propelled vehicle on a road, he would F3commit an offence under Article 15 or 16.

F4Paragraph (1) does not apply to the person if it ought reasonably to appear to the constable that there is no likelihood of his driving or attempting to drive a mechanically propelled vehicle whilst his ability to drive properly is impaired or whilst the proportion of alcohol in his breath, blood or urine exceeds the prescribed limit.

A person who is at a hospital as a patient shall not be arrested and taken from there to a police station in pursuance of this Article if it would be prejudicial to his proper care and treatment as a patient.

A constable must consult a medical practitioner on any question arising under this Article whether a person's ability to drive properly is or might be impaired through drugs and must act on the medical practitioner's advice.